CVE-2026-56099: OpenBSD mpls_do_error Kernel Stack Memory Disclosure via MPLS Input

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-06-18 · updated 2026-10-26
Weakness: CWE-125

Description

OpenBSD before commit 6a23123 (2026-06-18) contains an out-of-bounds read vulnerability in the mpls_do_error function within sys/netmpls/mpls_input.c that allows remote attackers to disclose kernel stack memory by sending crafted MPLS frames with 16 labels and no Bottom-of-Stack bit set.

Affected products

OpenBSD: before 2026-06-18 — fixed in 2026-06-18

How to fix

Upgrade to a fixed version: OpenBSD 2026-06-18. Check the vendor advisory for mitigations.

References

https://github.com/openbsd/src/commit/6a23123ec05f1eb29cfcaae0f3a468b2e1983cfd
https://pop.argus-systems.ai/advisory/adv-040.html
https://www.vulncheck.com/advisories/openbsd-mpls-do-error-kernel-stack-memory-disclosure-via-mpls-input
http://seclists.org/fulldisclosure/2026/Jun/17
http://www.openwall.com/lists/oss-security/2026/06/19/3

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