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CVE-2026-98393

N/A

Published 2026-10-14 · Last modified 2026-10-19

In the Linux kernel, the following vulnerability has been resolved: net: ipv4: Fix UDP length overflow with PMTU discover and big MTU This commit bounds cork->base.fragsize to IP_MAX_MTU to avoid a possible overflow of UDP length that triggers a WARN in udp_set_len_short when setsockopt IP_MTU_DISCOVER is set to IP_PMTUDISC_PROBE, and a large packet is sent over a netdev with an unusually large MTU. Steps to reproduce: 1. Set device MTU bigger than IP_MAX_MTU + 20. cork->base.fragsize will be set to that MTU in ip_setup_cork. 2. Set IP_MTU_DISCOVER to IP_PMTUDISC_PROBE. It lets maxnonfragsize be set to device MTU (cork->fragsize) in __ip_append_data, rather than to IP_MAX_MTU. 3. Send 65528 bytes of payload (+8 bytes of UDP header, +20 bytes of IPv4 header). Device MTU allows it (it's only one byte bigger than IP_MAX_MTU + IPv4 header, and the device MTU is bigger than that). 4. The UDP length in the built packet is 65536, which overflows the 16-bit length field and triggers the WARN in udp_set_len_short. Note: IP_PMTUDISC_DO with IPv4 is safe, because ip_dst_mtu_maybe_forward always clamps at IP_MAX_MTU, unlike ip6_dst_mtu_maybe_forward. The Fixes tag points at the first commit where I could reproduce the overflow with IPv4 and IP_PMTUDISC_PROBE.

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No known exploitation, public exploit, or elevated probability at this time. Track for changes.

Exploitation likelihood

0.2%chance of exploitation in 30 days · 10th percentile

○ In CISA KEV ○ Catalogued PoC

Impact if exploited

—CVSS · not scored

  • No impact metrics

Proof of concept

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Data snapshot:

Affected

Vendors Linux

Products Linux

Weakness (CWE)

Not classified.

CVSS vector

Not yet scored.

References and research data (JSON)

Vendor product assessments

Showing 32 of 277 vendor product statements; 245 omitted. Read the full vendor advisory.

  • kernel as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-64k-debug-modules-extra as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-64k-debug-modules-extra

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-debug-core as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-debug-core

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-doc as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-doc

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-64k-debug as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-64k-debug

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-64k-modules-extra as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-64k-modules-extra

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-debug-modules-extra as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-debug-modules-extra

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-uki-virt as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-uki-virt

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel.src as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel?arch=src

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-debug as a component of Red Hat Enterprise Linux 6 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-debug

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • no fix planned: Out of support scope
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • perf as a component of Red Hat Enterprise Linux 6 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/perf

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • no fix planned: Out of support scope
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-doc as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-doc

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-doc as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-doc

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel.src as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel?arch=src

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-debug as a component of Red Hat Enterprise Linux 8 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-debug

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-ipaclones-internal as a component of Red Hat Enterprise Linux 8 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-ipaclones-internal

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-debug-devel as a component of Red Hat Enterprise Linux 8 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-debug-devel

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-modules-internal as a component of Red Hat Enterprise Linux 8 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-modules-internal

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-zfcpdump-devel as a component of Red Hat Enterprise Linux 8 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-zfcpdump-devel

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-64k as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-64k

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-64k-debug-modules-internal as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-64k-debug-modules-internal

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-abi-stablelists as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-abi-stablelists

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-debug-modules-extra as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-debug-modules-extra

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-ipaclones-internal as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-ipaclones-internal

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-64k-debug as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-64k-debug

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-64k-debug-modules-partner as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-64k-debug-modules-partner

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-64k-modules-partner as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-64k-modules-partner

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-debug-modules-extra as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-debug-modules-extra

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-rt-modules-internal as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-rt-modules-internal

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-uki-virt-addons as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-uki-virt-addons

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • kernel-zfcpdump-modules-partner as a component of Red Hat Enterprise Linux 9 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/kernel-zfcpdump-modules-partner

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00
  • openshift/ose-rhel-coreos-9 as a component of Red Hat OpenShift Container Platform 4 · known affected

    Vendor assessment for this product only.

    pkg:oci/ose-rhel-coreos-9?repository_url=registry.redhat.io/openshift/ose-rhel-coreos-9

    • workaround: This issue can only be triggered on network devices configured with an MTU larger than IP_MAX_MTU (65535 bytes) while an application uses the IP_PMTUDISC_PROBE Path MTU discovery socket option. As a workaround, do not configure network interfaces with MTU values above 65535 bytes (for example, keep interfaces at standard values such as 1500); with such configurations the UDP length cannot overflow the 16-bit length field.
    • none available: Fix deferred
    Red Hat · CVE-2026-98393 · Updated 2026-10-18T08:29:18+00:00

References

Advisories

Technical & other

Sources: NVD · CVE.org · EPSS