CVE-2026-55785

Name of the Vulnerable Software and Affected Versions free5GC versions prior to 1.4.5

Description The AUSF component uses non-constant-time equality helpers for cryptographic authentication comparisons in internal/sbi/processor/ue authentication.go. Specifically, the Auth5gAkaComfirmRequestProcedure function compares RES* and XRES* using strings.EqualFold(), while the EapAuthComfirmRequestProcedure function compares AT MAC with XMAC using bytes.Equal() and evaluates XRES against RES using ordinary string equality. These comparisons can return at mismatch-dependent times, potentially creating a timing side channel, although HTTP/SBI noise makes remote exploitation difficult. Additionally, the 5G-AKA confirmation process logs the expected XRES* value at the INFO level, exposing sensitive authentication material to operators, log collectors, or any process with access to the AUSF logs.

Recommendations Update to version 1.4.5. As a temporary mitigation, restrict access to AUSF logs to prevent the exposure of XRES* authentication material. Replace strings.EqualFold(), bytes.Equal(), and == operators used for authentication values with constant-time comparison functions such as crypto/subtle.ConstantTimeCompare after normalizing input lengths and encodings.