CVE-2026-89550 - Vulnerability Details

- SUNRPC: svcauth_gss: enforce krb5 token minimum length

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;

Published: 2026-09-11

Score: 9.8 Critical

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

The Linux kernel’s SUNRPC authentication module enforces Kerberos security by unwrapping encrypted tokens. In the unwrapping routine, only an upper bound on the token length was previously checked, while the minimum length requirement for a valid RFC‑4121 token was omitted. A malicious actor can therefore send a token of 16 bytes or fewer; this value passes the upper‑bound test but triggers a divide‑by‑zero inside the kernel’s rotation function, resulting in a kernel panic. The vulnerability is classified as CWE‑369 and delivers a crash that brings the entire system down, effectively a denial‑of‑service to all users of the affected host.

Affected Systems

The flaw exists in any unpatched Linux kernel containing the original svcauth_gss implementation. Kernels released before the commit that added a minimum‑length check (commit 2eed1e6a) are vulnerable. Any distribution that has not yet merged this change into its kernel packages, or that packages an older kernel for stability reasons, remains at risk. System administrators should verify the kernel version on all nodes that run SUNRPC services and confirm the patch is present.

Risk and Exploitability

The CVSS score of 9.8 highlights the severity, while the EPSS score of less than 1 % indicates a low but non‑zero probability of exploitation. The vulnerability is not currently listed in CISA’s KEV catalog. An attacker would need to send a specially crafted, very short Kerberos token to a vulnerable SUNRPC service; no local privilege escalation or code execution is required. If successful, the exploit causes an immediate kernel crash and a denial‑of‑service condition for all users on the affected host.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`7c9fdcfb1b64c47ed618c103b617af3f86e1239c`	affected	< 0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd
`7c9fdcfb1b64c47ed618c103b617af3f86e1239c`	affected	< dd6afc6cab8c5d387d1ed2f069562ef7bdadd651
`7c9fdcfb1b64c47ed618c103b617af3f86e1239c`	affected	< de942dd8c2c8358bcad04ce44271954c48924423
`7c9fdcfb1b64c47ed618c103b617af3f86e1239c`	affected	< 2eed1e6a976a44015c3ee78841fe336796e2b21c
`7c9fdcfb1b64c47ed618c103b617af3f86e1239c`	affected	< a919c5c88769cf8fb3ec071e6078d830bf512489

Linux

affected

Version	Status	Constraints
`2.6.18`	affected	—
`0`	unaffected	< 2.6.18
`6.6.157`	unaffected	≤ 6.6.*
`6.12.109`	unaffected	≤ 6.12.*
`6.18.50`	unaffected	≤ 6.18.*
`7.2.4`	unaffected	≤ 7.2.*
`7.3-rc1`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[7c9fdcfb1b64c47ed618c103b617af3f86e1239c,dd6afc6cab8c5d387d1ed2f069562ef7bdadd651)`	affected	code_commit	—
`[7c9fdcfb1b64c47ed618c103b617af3f86e1239c,de942dd8c2c8358bcad04ce44271954c48924423)`	affected	code_commit	—
`[7c9fdcfb1b64c47ed618c103b617af3f86e1239c,2eed1e6a976a44015c3ee78841fe336796e2b21c)`	affected	code_commit	—
`[7c9fdcfb1b64c47ed618c103b617af3f86e1239c,a919c5c88769cf8fb3ec071e6078d830bf512489)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`2.6.18`	affected	semver	—
`[0,2.6.18)`	unaffected	semver	—
`[6.12.109,6.13.0)`	unaffected	semver	—
`[6.18.50,6.19.0)`	unaffected	semver	—
`[7.2.4,7.3.0)`	unaffected	semver	—
`[7.3-rc1,*]`	unaffected	generic	—

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Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade the Linux kernel to a version that includes commit 2eed1e6a or later, which introduces the minimum‑token length check.
If a kernel upgrade cannot be performed immediately, block external access to the SUNRPC port (default 111) so that only trusted hosts may contact the RPC service, or disable Kerberos authentication for that service until the kernel can be updated.
Consider disabling the RPC service entirely on systems that do not require it, or run a hardened proxy that validates Kerberos tokens before passing them to the kernel.

Generated by OpenCVE AI on September 15, 2026 at 21:58 UTC.

Tracking

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Advisories

Source	ID	Title
Debian DSA	DSA-6528-1	linux security update

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00671.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd
https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c
https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489
https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651
https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423
https://nvd.nist.gov/vuln/detail/CVE-2026-89550
https://www.cve.org/CVERecord?id=CVE-2026-89550

History

Mon, 14 Sep 2026 12:30:00 +0000

Type	Values Removed	Values Added
References		https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd

Sun, 13 Sep 2026 06:45:00 +0000

Type	Values Removed	Values Added
Metrics	cvssV3_1 `{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}`	cvssV3_1 `{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}`

Sat, 12 Sep 2026 00:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-369
References		https://nvd.nist.gov/vuln/detail/CVE-2026-89550 https://www.cve.org/CVERecord?id=CVE-2026-89550
Metrics	threat_severity `None`	cvssV3_1 `{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}` threat_severity `Important`

Fri, 11 Sep 2026 23:45:00 +0000

Type	Values Removed	Values Added
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;
Title		SUNRPC: svcauth_gss: enforce krb5 token minimum length
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489 https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651 https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-09-11T19:44:24.572Z

Updated: 2026-09-14T12:00:53.633Z

Reserved: 2026-09-11T19:38:34.723Z

Link: CVE-2026-89550

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-09-11T20:19:38.500

Modified: 2026-09-14T13:19:10.017

Link: CVE-2026-89550

Redhat

Severity : Important

Publid Date: 2026-09-11T19:44:24Z

Links: CVE-2026-89550 - Bugzilla

OpenCVE Enrichment

Updated: 2026-09-15T22:00:17Z

Weaknesses

CWE-369
Divide By Zero

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

Subscriptions

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