Vulnerability in Linux kernel (CVE-2026-89537)
Summary
Vulnerability in Linux kernel (CVE-2026-89537). Confidential information can be exposed externally.
Original description
The description as published by the source.
In the Linux kernel, the following vulnerability has been resolved:
SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2
gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags
byte at ptr[2], and padding at ptr[3..7], then passes
ptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg().
None of these accesses check read_token->len first.
The minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus
ctx->krb5e->cksum_len (12-24, depending on the enctype). All callers
accept shorter tokens from the wire:
-
gss_unwrap_resp_integ() enforces only an upper bound
(offset + len <= rcv_buf->len) before allocating
mic.data = kmalloc(len) and passing it to gss_verify_mic().
A malicious NFS server can therefore supply a short checksum
opaque, producing a small slab allocation that the Kerberos MIC
verifier reads past. -
gss_validate() enforces only len <= RPC_MAX_AUTH_SIZE (400)
before passing the wire-supplied length to
gss_validate_seqno_mic(), which constructs a mic xdr_netobj
and calls gss_verify_mic(). -
svcauth_gss_verify_header() enforces only
checksum.len >= XDR_UNIT (4 bytes) before dispatching to
gss_verify_mic(). -
svcauth_gss_unwrap_integ() checks only that the checksum fits
in gsd->gsd_scratch.
Add a length guard at the top of gss_krb5_verify_mic_v2(), before any
ptr[] access or scatterlist construction. Well-formed MIC tokens from
gss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_…
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-2026-89537 has been found in Linux kernel.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2026-89537" on the vendor's site.
CVE-2026-89537 (Linux kernel) — CVSS v3 9.1
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 9.1/10). Confidential information can be exposed externally.
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。
References
- web git.kernel.org
- web git.kernel.org
- web nvd.nist.gov
- web github.com
- web git.kernel.org