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CVE-2026-89538

SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: yes
  • Technical impact: total

Summary

In 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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: yes · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in ac9efc29346b6942e71f0e24a3178a9121330fab; From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in b5746095b59f4d11f39f08751d36bbdfd1e5deac; From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in 9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296; From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in 4abb44a29bb515df6f49123848765c70fc9b5021; From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in dfcd81ab45613d45996fbf483d4ef54b0ec90ab9; From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in 1f9856af065b6158271687e9788407b9573fd16f; From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in 880effc943ed82d6811f272ed3307c222b40f4d6; From cf4c024b908353fcc48309374d39e3399d67dfd1 · fixed in ad484748eec0a66eac0f13ab53b3fbedb7333c91

  • Linux Linux

    3.13

  • KernelLinux

    From 3.13.0 · fixed in 5.10.270; From 5.11.0 · fixed in 5.15.221; From 5.16.0 · fixed in 6.1.188; From 6.2.0 · fixed in 6.6.157; From 6.7.0 · fixed in 6.12.109; From 6.13.0 · fixed in 6.18.50; From 6.19.0 · fixed in 7.2.4

References 8

git.kernel.org