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CVE-2026-89538

Vulnérabilité critique dans Linux (Linux)

CVSS 9.8 · Critique
EPSS 0.7%
Linux•Linux•Versions : <880effc943ed82d6811f272ed3307c222b40f4d6, <=6.1.*, <ac9efc29346b6942e71f0e24a3178a9121330fab, <=6.12.*, <4abb44a29bb515df6f49123848765c70fc9b5021, 5.15.221, <3.13, <9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296, 5.10.270, 0, 7.2.4, 6.1.188, <1f9856af065b6158271687e9788407b9573fd16f, <=5.10.*, <=6.6.*, 6.6.157, <b5746095b59f4d11f39f08751d36bbdfd1e5deac, <ad484748eec0a66eac0f13ab53b3fbedb7333c91, 3.13, <=6.18.*, <=7.2.*, <dfcd81ab45613d45996fbf483d4ef54b0ec90ab9, <=*, <=5.15.*, cf4c024b908353fcc48309374d39e3399d67dfd1, 6.18.50, 6.12.109, 7.3

Description

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.

Gravité et risque d'exploitation

CVE-2026-89538 obtient un score CVSS de 9.8/10, soit une gravité critique. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.71 %, ce qui la place devant 52.8 % des CVE référencées.

Que faire ?

  • Vérifiez si Linux (versions <880effc943ed82d6811f272ed3307c222b40f4d6, <=6.1.*, <ac9efc29346b6942e71f0e24a3178a9121330fab, <=6.12.*, <4abb44a29bb515df6f49123848765c70fc9b5021, 5.15.221, <3.13, <9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296, 5.10.270, 0, 7.2.4, 6.1.188, <1f9856af065b6158271687e9788407b9573fd16f, <=5.10.*, <=6.6.*, 6.6.157, <b5746095b59f4d11f39f08751d36bbdfd1e5deac, <ad484748eec0a66eac0f13ab53b3fbedb7333c91, 3.13, <=6.18.*, <=7.2.*, <dfcd81ab45613d45996fbf483d4ef54b0ec90ab9, <=*, <=5.15.*, cf4c024b908353fcc48309374d39e3399d67dfd1, 6.18.50, 6.12.109, 7.3) est présent sur votre parc.
  • Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
  • À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
  • Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

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