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CVE-2026-89537

Critical Vulnerability: CVE-2026-89537

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).

Thursday, October 15, 2026Vulnios Threat Intelligence
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Vulnerability Snapshot

CVE-2026-89537 is rated CRITICAL — exploitation is trivial or already observed in the wild and impact is severe. Patch immediately, not on the next maintenance window.

Executive Summary

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_valida

Why It Matters

CVE-2026-89537 is rated CRITICAL severity, requiring immediate attention from security teams.

CVSS Base Score: 9.1/10

🛡️What Defenders Should Check

  • Check if you are affected — Review your asset inventory for products listed in CVE-2026-89537.
  • Apply available patches — Visit vendor advisories for the latest security updates.
  • Monitor for exploitation — Check your SIEM/IDS logs for related indicators.

    • Use Vulnios to continuously monitor your exposure to CVE-2026-89537 and similar vulnerabilities.

    References & Sources

  • https://git.kernel.org/stable/c/7a946b2e7207f968902f2147ab9b30726f82f7ab
  • https://git.kernel.org/stable/c/996dd15f60121bdd7896b4554458f8806d608063
  • https://git.kernel.org/stable/c/b94f6719dcd9f7a609bc5f459f85795900e77d25

    • How Vulnios Detects This

    Vulnios scans for this vulnerability using Trivy and Grype for SBOM-based CVE matching and Vulnios CVE feed continuous monitoring against your asset inventory. Run a scan against your environment to see whether you are exposed; findings are linked back to the original CVE record so triage starts with the patch path already known.

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    Sources

    Related Threat Alerts

    Frequently Asked Questions

    What is CVE-2026-89537?

    CVE-2026-89537 is a critical-severity vulnerability tracked under the Common Vulnerabilities and Exposures program. 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 f

    Am I affected?

    Affected technology is listed in the Affected Products section above. If your asset inventory contains any of them, assume in-scope until you can prove otherwise.

    How urgent is the response?

    Critical: do not wait for your normal patch cycle. Verify exposure today, apply the vendor patch immediately, and add detection rules for any post-exploit indicators.

    How do I remediate?

    Apply the vendor patch listed in the upstream advisory linked under Sources. If the patch is not yet available, follow the vendor-supplied workaround (often a config flag or feature disable) and add detections for the published exploit pattern in your SIEM. Re-scan after the patch lands to confirm the finding clears.

    Where can I track exploitation activity?

    Watch CISA's Known Exploited Vulnerabilities catalog for CVE-2026-89537. Cross-reference with public exploit databases and your own SIEM/IDS for indicator-of-compromise patterns. Vulnios tracks KEV status automatically and surfaces it on the asset findings view.

    How does Vulnios help with this?

    Vulnios continuously cross-references your asset inventory against the live CVE feed (NVD, vendor advisories, CISA KEV, and curated OSINT). When a new CVE matches your environment, you get a prioritized finding with the severity, KEV status, exploit-prediction (EPSS), and a direct path to the vendor patch. You can start a free scan from the homepage.

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