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CVE-2026-46033 Linux CVE debrief

A vulnerability in the Linux kernel's authencesn crypto driver allowed creation of AEAD transforms with invalid default authentication sizes when paired with hash algorithms having digest sizes of 1-3 bytes. The ESN (Extended Sequence Number) code paths require at least 4 bytes of authentication tag space to handle high-order sequence number data. While explicit setauthsize() calls rejected invalid sizes, the transform creation path failed to validate the ahash digest size when initializing the default authsize. This could lead to out-of-bounds memory access when AF_ALG users triggered ESN operations on such misconfigured transforms. The fix adds validation during instance creation to reject ahash digest sizes in the invalid 1-3 byte range.

Vendor
Linux
Product
Unknown
CVSS
Unknown
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-27
Original CVE updated
2026-05-27
Advisory published
2026-05-27
Advisory updated
2026-05-27

Who should care

Linux system administrators, kernel maintainers, container platform operators, and security teams monitoring crypto API attack surface in multi-tenant environments

Technical summary

The authencesn AEAD template in Linux kernel crypto subsystem failed to validate ahash digest sizes during transform instantiation. When combined with algorithms like cbcmac(cipher_null) producing 1-3 byte digests, the resulting transform inherited an invalid default authsize that the ESN encrypt/decrypt paths would use to access 4 bytes of sequence number data at the end of authenticated regions. This caused out-of-bounds memory access. The vulnerability was exploitable through AF_ALG sockets where unprivileged users could instantiate such transforms. The fix enforces minimum 4-byte digest size requirement (or zero) during crypto_authenc_esn_create(), preventing instantiation of vulnerable transform configurations.

Defensive priority

medium

Recommended defensive actions

  • Apply kernel updates containing the referenced stable commits when available for your distribution
  • Verify crypto API usage does not rely on authencesn with cbcmac(cipher_null) or similar short-digest ahash algorithms
  • Monitor vendor security advisories for kernel package updates addressing CVE-2026-46033
  • Review AF_ALG socket usage in containerized environments where unprivileged crypto access may be exposed

Evidence notes

CVE description confirms the vulnerability exists in crypto: authencesn and was resolved by rejecting short ahash digests during instance creation. Multiple stable kernel commits are referenced, indicating backports to supported branches. No CVSS score or severity assigned yet per NVD status 'Awaiting Analysis'.

Official resources

2026-05-27