In the jose package before 0.11.0 for OCaml, library calls to validate an RSA signature only confirm that PKCS #1

Published September 10, 2026 CVE-2026-89086

OCaml's jose package can accept altered tokens as genuine because it does not properly check RSA signatures. An attacker could change signed information without the application detecting it.

Severity
CriticalCVSS 3.1 · 9.1
Fix
Fixed in 0.11.0
Affected versions
before 0.11.0
Weakness
CWE-347Improper Verification of Cryptographic Signature
Exploit likelihood
0.20% in 30 daysEPSS, higher than 10% of known flaws
Affects
jose
Exploited
Not confirmedPublic proof of concept, per CISA SSVC
CISA SSVC
Proof of concept publicAutomatable: yes · Technical impact: total
EU ID
EUVD-2026-75708ENISA vulnerability database

How it works

  • An attacker supplies a token whose contents differ from the originally signed data. jose checks whether the signature has the expected format, but does not verify it against the public key.
  • The application can then accept the altered token as valid.

What to do

Check the installed jose package version and compare it with 0.11.0. Versions below 0.11.0 are affected.

Upgrade jose to version 0.11.0 or later.

Technical details

CVE-2026-89086 affects the opam jose package before 0.11.0. RSA signature validation confirms PKCS 1 decoding but skips verification with the public key, allowing altered signed data to be accepted.

Severity breakdown

  • Attack vector Network Requires network access to the vulnerable service
  • Attack complexity Low Low complexity under the assessed conditions
  • Privileges required None Attacker needs no account or login
  • User interaction None No victim action needed
  • Scope Unchanged Impact stays within the same security authority
  • Confidentiality impact High Sensitive data can be exposed with serious impact
  • Integrity impact High Protected data can be changed with serious impact
  • Availability impact None No availability impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N Open in FIRST.org calculator

References

View Original Source