Vulnerability in Linux kernel (CVE-2026-89542)
Summary
Vulnerability in Linux kernel (CVE-2026-89542). Successful exploitation can lead to full system takeover.
Original description
The description as published by the source.
In the Linux kernel, the following vulnerability has been resolved:
SUNRPC: harden gss_krb5_unwrap_v2 against short tokens
gss_krb5_unwrap_v2() reads the EC and RRC header fields at ptr+4 and
ptr+6 before validating that the token is at least GSS_KRB5_TOK_HDR_LEN
(16) bytes long, and its rotate_left() helper passes buf->len - base
to xdr_buf_subsegment() without verifying that base <= buf->len. When
a caller hands in a sub-16-byte token, or a token whose declared len
leaves base past the end of the buffer, three distinct failures follow:
gss_krb5_unwrap_v2(offset, len, buf)
ptr = buf->head[0].iov_base + offset
ec = *(ptr + 4) /* OOB read on short head */
rrc = *(ptr + 6) /* OOB read on short head */
rotate_left(offset + 16, buf, rrc)
xdr_buf_subsegment(buf, &subbuf,
base, buf->len - base) /* u32 wrap when base > len */
_rotate_left(&subbuf, shift)
shift %= buf->len /* divide-by-zero when base == len */
After decryption, the cleanup arithmetic has the same shape:
movelen = min_t(unsigned int, buf->head[0].iov_len, len);
movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip;
BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen >
buf->head[0].iov_len);
The BUG_ON re-adds the value just subtracted, so it reduces to
min(A, B) > A and is permanently false; it cannot catch the unsigned
underflow of move…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-89542 has been found in Linux kernel.
Successful exploitation can lead to full system takeover. CVSS score: 9.8/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2026-89542" on the vendor's site.
CVE-2026-89542 (Linux kernel) — CVSS v3 9.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (unclassified) exists in Linux kernel.
Check the vendor advisory for the affected versions of Linux kernel.
Severity: Critical (CVSS 9.8/10). Successful exploitation can lead to full system takeover.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで Linux kernel を使っているサービスとバージョンを洗い出す。
-
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Ubuntu UBUNTU-CVE-2026-89542 linux
References
- advisory nvd.nist.gov
- advisory github.com
- package git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web github.com