CVE-2026-9648
The crypton-x509-validation Haskell library fails to enforce X.509 NameConstraints, allowing TLS clients to accept certificates whose Subject Alternative Names fall outside the issuing CA’s permitted subtrees.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.22%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
The crypton-x509-validation Haskell library fails to enforce X.509 NameConstraints, allowing TLS clients to accept certificates whose Subject Alternative Names fall outside the issuing CA’s permitted subtrees. This oversight enables an attacker who compromises a name-constrained sub-CA to impersonate domains beyond its intended scope.
- CVSS 3.1
- 9.1 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- EPSS
- 0.22% probability · 13th percentile
- CISA KEV
- Not listed
- Source
- cret@cert.org
References
- https://github.com/haskell/security-advisories/pull/332
- https://github.com/kazu-yamamoto/crypton-certificate/pull/30
- https://github.com/kazu-yamamoto/crypton-certificate/pull/30/changes/f4b77edf6ead77f4a886da40e41eab20f0180e39
- https://hackage.haskell.org/package/crypton-x509-validation-1.9.1/revisions/
- https://www.kb.cert.org/vuls/id/862559
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.