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VulnerabilityPublished Updated

CVE-2026-91096: Facebook proxygen · Use After Free

Affects Facebook proxygenSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to v2026.09.28.00 soon.

Data as of 12 Nov 2026, 23:25 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 17% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in v2026.09.28.00, 2026.09.28.00
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 28 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

What to do

Upgrade proxygen to v2026.09.28.00; facebook/proxygen to 2026.09.28.00.

Affected software

ProductAffectedFixed in
FacebookproxygenAffected
  • >=2024.10.28.00 <2026.09.28.00
Fixed in
  • v2026.09.28.00
GitHubfacebook/proxygenpkg:github/facebook/proxygenOther threatsAffected
  • >=2024.10.28.00 <2026.09.28.00
Fixed in
  • 2026.09.28.00

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

CVE-2026-91096 is a use-after-free vulnerability in Facebook's proxygen library affecting versions from 2024.10.28.00 up to but not including 2026.09.28.00. The issue arises because the WebTransportImpl component fails to unregister read callbacks for streams that are no longer open before destroying them, potentially allowing the transport to invoke a freed read callback. This vulnerability has a high severity rating with a CVSS score of 7.5, indicating a significant impact on confidentiality without affecting integrity or availability.

References

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