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CVE-2026-43139 Linux CVE debrief

A vulnerability in the Linux kernel's xfrm6 component can cause an uninitialized source address to be used, potentially leading to unintended behavior. This issue arises from the xfrm6_get_saddr() function not properly checking the return value of ipv6_dev_get_saddr(), resulting in the use of an uninitialized address in certain scenarios. The vulnerability can lead to unexpected behavior, emphasizing the need for thorough validation and patching. Linux kernel developers and maintainers should assess their exposure and apply patches as necessary. The vulnerability's impact is significant, with a CVSS score of 8.6, indicating high severity. Affected systems may experience unintended

Vendor
Linux
Product
Unknown
CVSS
HIGH 8.6
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-06
Original CVE updated
2026-10-19
Advisory published
2026-05-06
Advisory updated
2026-10-19

Who should care

Linux kernel developers and maintainers, as well as users of Linux-based systems, should assess their exposure to this vulnerability and apply patches as necessary. System administrators and security teams responsible for Linux-based systems should also be aware of this vulnerability and take steps to mitigate its impact. Additionally, organizations using Linux-based systems should review their configurations and ensure that proper address initialization

Why it matters

A vulnerability in the Linux kernel's xfrm6 component can cause an uninitialized source address to be used, potentially leading to unintended behavior.

  • Verify source address initialization to prevent unintended behavior.
  • Assess Linux kernel version and apply patches to prevent exploitation.
  • Monitor system logs for potential exploitation attempts.

Technical summary

The vulnerability is caused by the xfrm6_get_saddr() function not checking the return value of ipv6_dev_get_saddr(). When ipv6_dev_get_saddr() fails to find a suitable source address, it returns -EADDRNOTAVAIL, but xfrm6_get_saddr() still returns 0 (success), leading to the use of an uninitialized address. This issue can be addressed by properly checking the return value of ipv6_dev_get_saddr() and ensuring that the source address is initialized before use. The vulnerability's technical impact is significant, as it can lead to

Defensive priority

Medium

Recommended defensive actions

  • Review and apply the provided patches to ensure the vulnerability is addressed.
  • Verify the Linux kernel version and update to a patched version if necessary.
  • Monitor system logs for potential exploitation attempts.
  • Perform a thorough review of system configurations to ensure proper address initialization.
  • Conduct regular security audits to identify potential vulnerabilities.
  • Implement compensating controls for exposed systems while remediation is scheduled and verified.
  • Track exceptions and retest remediated assets to ensure the vulnerability is fully resolved.

Evidence notes

The vulnerability is caused by the xfrm6_get_saddr() function not checking the return value of ipv6_dev_get_saddr(). When ipv6_dev_get_saddr() fails to find a suitable source address, it returns -EADDRNOTAVAIL, but xfrm6_get_saddr() still returns 0 (success), leading to the use of an uninitialized address.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-43139 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-43139

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

  • CVE-2026-43139 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-43139

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

Supplemental references

  • xfrm6: fix uninitialized saddr in xfrm6_get_saddr()

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/43xxx/CVE-2026-43139.json

    cve_program_cvelist_v5

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/4f28141786e1fe884ce42a5197ba9beed540f0ea

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/6535867673bf301d52aa00593a4d1d18cc3922fa

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/eb2ee15290af14c60b45cf2b73f5687d1d077d9b

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/719918fc88df6da023dfff370cd965151a5afd7f

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/dc0abce055134cb83b0d981d31ceb20dda419787

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/c7221e7bd8fc2ef38a0b27be580d9d202281306b

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/3dcd1664ac15eee6a690daec7c4ffc59190406f7

    Supplemental source

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.