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CVE-2026-85534

MEDIUM 5.9 ALL-YEARS

Published 2026-09-04 · Last modified 2026-09-04 · redhat · NVD: Awaiting Analysis

A flaw was found in libsoup. When a client sends an HTTP/2 request body from a non-pollable input stream, the library can buffer more data than the current flow-control window later allows. A malicious HTTP/2 server can shrink SETTINGS_INITIAL_WINDOW_SIZE while that buffered read is still in progress. The client then copies the full buffer into a smaller DATA callback without a runtime bounds check, which can abort the process or fail the HTTP/2 session.

LIMITED SIGNALS

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

Exploitation likelihood

0.3%chance of exploitation in 30 days · 24th percentile

○ In CISA KEV○ Catalogued PoC◆ SSVC: exploitation none, automatable no

Impact if exploited

5.9CVSS 3.1 · MEDIUM · CNA

  • ConfidentialityNone
  • IntegrityNone
  • AvailabilityHigh

What an attacker needs

  • ✓Access: Reachable over the network — no local access needed
  • ✓Privileges: No account or privileges required
  • ✓User interaction: No user interaction needed
  • ⚠Complexity: Needs a race window or specific setup

✓ lowers the bar for an attacker · ⚠ raises it

Proof of concept

No public PoC is currently catalogued.

Search for new PoCs

Search GitHub now — results may be empty or unverified.

Tracked sources are checked weekly for the full archive, including PoCs published after the original disclosure. A later release appears after a tracked source lists it and a refresh succeeds.

Affected

Vendors Red Hat

Products Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 6 Red Hat Enterprise Linux 7 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 9

Weakness (CWE)

  • CWE-617: Reachable Assertion

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References and research data (JSON)

Vendor product assessments

  • libsoup3 as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/libsoup3

    • workaround: Do not HTTP/2-upload from non-pollable streams (e.g. GFileInputStream) to untrusted servers. soup_message_set_request_body_from_bytes() is the pollable path. Assertions abort instead of returning an oversized length; that is not a fix.
    • none available: Fix deferred
    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup3-devel as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/libsoup3-devel

    • workaround: Do not HTTP/2-upload from non-pollable streams (e.g. GFileInputStream) to untrusted servers. soup_message_set_request_body_from_bytes() is the pollable path. Assertions abort instead of returning an oversized length; that is not a fix.
    • none available: Fix deferred
    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup3-doc as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/libsoup3-doc

    • workaround: Do not HTTP/2-upload from non-pollable streams (e.g. GFileInputStream) to untrusted servers. soup_message_set_request_body_from_bytes() is the pollable path. Assertions abort instead of returning an oversized length; that is not a fix.
    • none available: Fix deferred
    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup3.src as a component of Red Hat Enterprise Linux 10 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/libsoup3?arch=src

    • workaround: Do not HTTP/2-upload from non-pollable streams (e.g. GFileInputStream) to untrusted servers. soup_message_set_request_body_from_bytes() is the pollable path. Assertions abort instead of returning an oversized length; that is not a fix.
    • none available: Fix deferred
    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup-devel as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup-devel

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup.src as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup?arch=src

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup-devel as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup-devel

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup.src as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup?arch=src

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup-devel as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup-devel

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup.src as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup?arch=src

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup as a component of Red Hat Enterprise Linux 9 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup-devel as a component of Red Hat Enterprise Linux 9 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup-devel

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00
  • libsoup.src as a component of Red Hat Enterprise Linux 9 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/libsoup?arch=src

    Red Hat · CVE-2026-85534 · Updated 2026-09-04T10:41:54+00:00

All CVSS metrics

  • MEDIUM 5.9 v3.1 · CNA Primary
    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  • MEDIUM 5.9 v3.1 · NVD Secondary
    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References

Advisories

Technical & other

Sources: NVD · CVE.org · All sources and attribution · EPSS