SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89538
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:36 UTC
Updated2026-09-11 20:19:36 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field gss_krb5_unwrap_v2() sets buf->len to a logical length, which can be much smaller than head[0].iov_len (the allocated receive-page capacity). It then calls xdr_buf_trim() with a trim length derived from the 16-bit "extra count" (ec) field in the Kerberos v2 token header. The ec field is authenticated by the post-decrypt memcmp() against the encrypted header copy, so a randomly-mutated value is rejected. However, any peer holding a valid GSS context can legitimately encrypt a token whose ec exceeds the plaintext length. Per RFC 4121, such a token is structurally malformed. Although xdr_buf_trim() now clamps the buf->len subtraction to avoid unsigned underflow, the buffer is still left in a semantically invalid state (zero length, inconsistent iov lengths) when ec is oversized. Reject these tokens before calling xdr_buf_trim(), giving callers a well-defined GSS_S_DEFECTIVE_TOKEN error and keeping the xdr_buf internally consistent. The wrapped blob begins at a nonzero offset -- both callers pass len as offset + opaque_len -- so buf->len still counts the offset bytes that precede the blob. Compare the trim length against the remaining wrapped segment, buf->len - offset, rather than the whole buffer; comparing against buf->len alone leaves an offset-wide window in which an oversized ec passes the test and xdr_buf_trim() cuts into the bytes ahead of the blob.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected cf4c024b908353fcc48309374d39e3399d67dfd1 dfcd81ab45613d45996fbf483d4ef54b0ec90ab9 git Not specified
CNA Linux Linux affected cf4c024b908353fcc48309374d39e3399d67dfd1 1f9856af065b6158271687e9788407b9573fd16f git Not specified
CNA Linux Linux affected cf4c024b908353fcc48309374d39e3399d67dfd1 880effc943ed82d6811f272ed3307c222b40f4d6 git Not specified
CNA Linux Linux affected cf4c024b908353fcc48309374d39e3399d67dfd1 ad484748eec0a66eac0f13ab53b3fbedb7333c91 git Not specified
CNA Linux Linux affected 3.13 Not specified
CNA Linux Linux unaffected 3.13 semver Not specified
CNA Linux Linux unaffected 6.12.109 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.50 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/1f9856af065b6158271687e9788407b9573fd16f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/dfcd81ab45613d45996fbf483d4ef54b0ec90ab9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/880effc943ed82d6811f272ed3307c222b40f4d6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ad484748eec0a66eac0f13ab53b3fbedb7333c91 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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