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CVE-2026-84970

MEDIUM 5.9

Published 2026-09-03 · Last modified 2026-09-03

A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.

NO EXPLOITATION SIGNALS

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

Exploitation likelihood

0.1%chance of exploitation in 30 days · 1st percentile

○ In CISA KEV ○ Public exploit / PoC

Impact if exploited

5.9CVSS 4.0 · MEDIUM

  • ConfidentialityLow
  • IntegrityLow
  • AvailabilityHigh

What an attacker needs

  • ⚠Access: Requires local access to the host
  • ✓Privileges: No account or privileges required
  • ✓User interaction: No user interaction needed
  • ✓Complexity: No special conditions — reliably repeatable
  • ⚠Requirements: Specific conditions must be present

✓ lowers the bar for an attacker · ⚠ raises it

Proof of concept & exploit code

Test against your own equipment

curl -s https://vulnpedia.com/cve/CVE-2026-84970/poc.jsonMachine-readable PoC index for this CVE (for automation).

Listed for defensive triage, patch verification, and authorized testing on systems you own. Machine-readable: /cve/CVE-2026-84970/poc.json

Affected

Vendors Mongodb

Products C++ Driver

Weakness (CWE)

  • CWE-681: : Incorrect Conversion between Numeric Types

CVSS vector

CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N

All CVSS metrics

  • MEDIUM 5.9 v4.0 · CNA Primary
    CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
  • MEDIUM 6.2 v3.1 · CNA Primary
    CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  • MEDIUM 5.9 v4.0 · NVD Secondary
    CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
  • MEDIUM 6.2 v3.1 · NVD Secondary
    CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

References

Technical & other

Sources: NVD · CVE.org · EPSS