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CVE-2026-89555

Critical Vulnerability: CVE-2026-89555

In the Linux kernel, the following vulnerability has been resolved: mpls: reload header after pskb_may_pull() mpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop when an MPLS route has multiple nexthops. While walking the MPLS label stack, the hash routine caches hdr for the current label. After finding the bottom-of-stack label, it calls pskb_may_pull() before reading the inner IP header. If an skb is constructed with the inner IP header in nonlinear data and insufficie

Monday, September 14, 2026Vulnios Threat Intelligence
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Vulnerability Snapshot

CVE-2026-89555 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:

mpls: reload header after pskb_may_pull()

mpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop

when an MPLS route has multiple nexthops. While walking the MPLS label

stack, the hash routine caches hdr for the current label. After finding

the bottom-of-stack label, it calls pskb_may_pull() before reading the

inner IP header.

If an skb is constructed with the inner IP header in nonlinear data and

insufficient tailroom in the linear head, pskb_may_pull() calls

pskb_expand_head() to replace the skb head and free the old one. This

leaves hdr pointing to freed memory. The IPv6 path can invalidate hdr

again when it performs a second pull for the larger header.

The issue was found through static analysis. A reproducer sending a legal

Geneve packet through a bareudp/MPLS multipath setup triggered the same

KASAN report in 2 of 2 unpatched runs:

BUG: KASAN: slab-use-after-free in mpls_select_multipa

Why It Matters

CVE-2026-89555 is rated CRITICAL severity, requiring immediate attention from security teams.

CVSS Base Score: 9.8/10

🛡️What Defenders Should Check

  • Check if you are affected — Review your asset inventory for products listed in CVE-2026-89555.
  • 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-2026-89555 and similar vulnerabilities.

    References & Sources

  • https://git.kernel.org/stable/c/29e63b8d9fc150cc191b1c6eb7e16e1247e1b650
  • https://git.kernel.org/stable/c/49d38c1b4390412f8950d33dfaee0ccbd17beb81
  • https://git.kernel.org/stable/c/aa4fe0b450a461aa1162fe8375f5d28f4c957df8
  • https://git.kernel.org/stable/c/b1c0783b2facc398437ad8f8b86c636d7a78f8db
  • https://git.kernel.org/stable/c/bfaaff99238326166694354a63a76c02563f98b1
  • https://git.kernel.org/stable/c/d82b90a38c2ca8a0694428eab0e9551c23f2447d
  • https://git.kernel.org/stable/c/d9640239827d6d0cb84263b590f7a4f1596c17eb
  • https://git.kernel.org/stable/c/fed638a248116b8a249bd4202d28e5934bdc65ad

    • 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-2026-89555?

    CVE-2026-89555 is a critical-severity vulnerability tracked under the Common Vulnerabilities and Exposures program. In the Linux kernel, the following vulnerability has been resolved:

    mpls: reload header after pskb_may_pull()

    mpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop

    when an MPLS rou

    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-2026-89555. 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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