CVE-2026-89550
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, svcauth_gss_unwrap_priv() only validated an upper bound on the wire-supplied opaque length before passing the buffer to gss_unwrap(), with no minimum length check. A token of 16 bytes or less (the RFC 4121 header size) reached gss_krb5_unwrap_v2(), where header reads ran past the token and rotate_left() could divide by zero. The fix adds a minimum-length check before the token reaches the krb5 unwrap core.
Risk Assessment
A remote attacker can send a specially crafted, too-short krb5 token to a SUNRPC service using GSS authentication, triggering a divide-by-zero and kernel crash (denial of service). In environments with NFS or other RPC services using Kerberos, this can lead to service unavailability.
Recommendation
Update the Linux kernel to a version containing the fix that enforces a minimum krb5 token length (rejecting tokens with length <= GSS_KRB5_TOK_HDR_LEN). Until the patch is applied, consider restricting access to RPC/GSS services from untrusted networks.
Other vulnerabilities in Linux kernel
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: SUNRPC: svcauth_gss: enforce krb5 token minimum length svcauth_gss_unwrap_priv() validates only an upper bound on the wire-supplied opaque length before handing the buffer to gss_unwrap(): if (len > xdr_stream_remaining(xdr)) goto unwrap_failed; offset = xdr_stream_pos(xdr); ... maj_stat = gss_unwrap(ctx, offset, offset + len, buf); The wire value `len` flows unchanged as the upper bound into the krb5 unwrap path, so a len in [0, 16] passes this check and is handed to gss_unwrap(). For a krb5 v2 context that lands in gss_krb5_unwrap_v2(), which reads the 16-byte RFC 4121 token header fields at ptr+4 and ptr+6 and then calls rotate_left() before any integrity check. With a sub-header length the header reads run past the token, and _rotate_left()'s `shift %= buf->len` path can divide by zero when buf->len has been driven to zero by the truncated token. A header-only token (len == 16) is equally invalid: with a non-zero RRC field and the opaque blob ending at the XDR buffer boundary, rotate_left() builds a zero-length subbuffer, reaching the same division. Reject the token at the server entry point before it reaches the krb5 unwrap core. A valid sealed RFC 4121 token must contain the 16-byte header plus at least some encrypted payload. Fix by adding a minimum-length check immediately after the existing upper-bound check: if (len <= GSS_KRB5_TOK_HDR_LEN) goto unwrap_failed;