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PatchSiren cyber security CVE debrief

CVE-2026-45847 Linux CVE debrief

A vulnerability in the Linux kernel's networking stack has been resolved. The issue involved a WARN_ON_ONCE assertion that could be triggered when accessing the forward path array. Recent support for IPIP tunnels increased the likelihood of reaching this warning if userspace constructed a sufficiently long forward path. The fix removes this WARN_ON_ONCE to prevent unnecessary kernel warnings under legitimate but uncommon network configurations.

Vendor
Linux
Product
Unknown
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-27
Original CVE updated
2026-06-25
Advisory published
2026-05-27
Advisory updated
2026-06-25

Who should care

Linux system administrators running kernels with IPIP tunnel support, particularly those with complex network topologies or nested tunnel configurations

Technical summary

The Linux kernel contained a WARN_ON_ONCE assertion in the networking forward path array access code. With the addition of IPIP tunnel support, userspace could construct network configurations with sufficiently long forward paths that would trigger this warning. While not a security vulnerability in the traditional sense (no memory corruption or privilege escalation), the warning could cause log spam and potential operational issues. The resolution removes the WARN_ON_ONCE entirely. Multiple stable kernel branches received backports of this fix.

Defensive priority

medium

Recommended defensive actions

  • Apply kernel updates from your Linux distribution that include the referenced stable commits
  • Monitor for kernel package updates addressing this issue
  • Review IPIP tunnel configurations for unusual forward path lengths

Evidence notes

The CVE description indicates this was a code quality fix to remove a WARN_ON_ONCE that could be triggered by valid IPIP tunnel configurations. Multiple stable kernel commits are referenced, suggesting backports to various kernel versions.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-45847 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-45847

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-45847 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-45847

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/008e7a7c293b30bc43e4368dac6ea3808b75a572

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/50422613185d505201167e8bdd2f2700790d5db6

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/548244c2f542aa0ad49453e9306e715a3877bc44

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/9464ca7a6e56ad1ebf48b2ad5c16871edfad10c6

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/959ea349c7e2d4edf07b6838ca7e59345fe61a08

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/a78d055ba7c31103ad02f8eceb0c452e154d2660

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/dcf9b3c90e5560339649d088836529883fb509f3

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.