CVE-2026-89550: Linux Vulnerability (CVSS 9.8)

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;

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.46%

38.8th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c, < 0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd; >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c, < dd6afc6cab8c5d387d1ed2f069562ef7bdadd651; >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c, < de942dd8c2c8358bcad04ce44271954c48924423; >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c, < 2eed1e6a976a44015c3ee78841fe336796e2b21c; >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c, < a919c5c88769cf8fb3ec071e6078d830bf512489
Linux	Linux	2.6.18

References

Timeline

Published: Sep 11, 2026
Last Modified: Sep 14, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-89550?

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;

How severe is CVE-2026-89550?

CVE-2026-89550 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.46% probability of exploitation in the next 30 days.

How do I fix CVE-2026-89550?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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