CVE-2026-89550

Description

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;

Gravité et risque d'exploitation

CVE-2026-89550 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 0.46 %, ce qui la place devant 38.3 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.12.*, 2.6.18, 0, 7.2.4, <2.6.18, <2eed1e6a976a44015c3ee78841fe336796e2b21c, <=6.6.*, 6.6.157, <de942dd8c2c8358bcad04ce44271954c48924423, <=6.18.*, <0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd, <=7.2.*, <=*, 7c9fdcfb1b64c47ed618c103b617af3f86e1239c, 6.18.50, <dd6afc6cab8c5d387d1ed2f069562ef7bdadd651, 6.12.109, <a919c5c88769cf8fb3ec071e6078d830bf512489, 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

• https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd
• https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651
• https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423
• https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c
• https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489