critical 9.8

CVE-2026-89538 in the critical feed json

SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field

published 2026-09-11 58 d ago modified 2026-10-19 21 d ago also EUVD-2026-76449

cvss: 9.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.7%; EPSS 0.7% chance of exploitation in 30 days, percentile 53%
public exploits: 0; none known

In the Linux kernel, the following vulnerability has been resolved:

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.

Patch / fix

fixed in 1 distros 5 links 8

Linux Linux 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4, 7.3

debian ubuntu suse opensuse azure linux

linux Debian 12 6.1.190-1
linux Debian 13 6.12.111-1
linux Debian 14 7.2.6-1
linux-6.12 Debian 12 6.12.111-1~deb12u1

debian advisories DEBIAN-CVE-2026-89538

linux Ubuntu 22.04 LTS 5.15.0-202.212
linux Ubuntu 26.04 LTS 7.0.0-42.42
linux-aws Ubuntu 22.04 LTS 5.15.0-1119.126
linux-aws Ubuntu 26.04 LTS 7.0.0-1016.17
linux-gcp Ubuntu 22.04 LTS 5.15.0-1120.130
linux-gcp Ubuntu 26.04 LTS 7.0.0-1016.18
linux-gke Ubuntu 22.04 LTS 5.15.0-1115.121
linux-ibm Ubuntu 22.04 LTS 5.15.0-1113.117

ubuntu advisories UBUNTU-CVE-2026-89538

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.84.1
kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.84.1
kernel-zfcpdump SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
kernel-obs-build SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
kernel-default-base SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1.150700.17.47.1

suse advisories SUSE-SU-2026:4706-1 SUSE-SU-2026:4687-1 SUSE-SU-2026:4640-1 SUSE-SU-2026:24316-1 SUSE-SU-2026:24315-1 SUSE-SU-2026:24181-1

kernel-rt openSUSE Leap 16.0 6.12.0-160000.39.1
dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.39.1
kernel-64kb openSUSE Leap 16.0 6.12.0-160000.39.1
kernel-syms openSUSE Leap 16.0 6.12.0-160000.39.1
kernel-azure openSUSE Leap 16.0 6.12.0-160000.39.1
kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.39.1
kernel-source openSUSE Leap 16.0 6.12.0-160000.39.1
kernel-default openSUSE Leap 16.0 6.12.0-160000.39.1

opensuse advisories openSUSE-SU-2026:22091-1 openSUSE-SU-2026:11880-1

kernel Azure Linux 3.0 6.6.157.1-1

azure linux advisories AZL-100070

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-89538 updated 2026-11-06 cvss 6.5

kernel: SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field

Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
affected: workaround, no fix planned “Out of support scope”
Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: total
Assessed: 23 d ago (2026-10-16)

Exploit prediction

0.71% chance of exploitation in the next 30 days, higher than 53% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Linux Linux

Classification

Technology feeds

Linux kernel rss critical rss

References

Sources

CVE List CVE-2026-89538
NVD CVE-2026-89538

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary