CVE-2026-56099: OpenBSD before commit 6a23123 (2026-06-18) contains an out-of-bounds read vulnerability in the mpls_do_error f

Q: How do I fix CVE-2026-56099?

openbsd: upgrade to 2026-06-18. Exact commands for each OS are on this page.

Q: Is CVE-2026-56099 being exploited?

CVE-2026-56099 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-56099 affect?

CVE-2026-56099 affects openbsd. Severity is medium (CVSS 5.3). 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 frame

Q: How urgent is CVE-2026-56099?

Priority 39/100. Public exploit reference; Remotely exploitable, no login, no user action

This week

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-56099 is a medium-severity flaw (CVSS 5.3) affecting openbsd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-125
Published	2026-06-18
Last modified	2026-10-26

Publisher (CNA): VulnCheck · Vendor: openbsd

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-18 20:16 UTCPublished CVE record published
2026-10-26 11:10 UTCUpdated Record last modified

openbsd openbsd UPGRADE

Affected: < 2026-06-18

Fixed in: 2026-06-18

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-56099?

openbsd: upgrade to 2026-06-18. Exact commands for each OS are on this page.

Is CVE-2026-56099 being exploited?

CVE-2026-56099 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-56099 affect?

CVE-2026-56099 affects openbsd. Severity is medium (CVSS 5.3). 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 frame

How urgent is CVE-2026-56099?

Priority 39/100. Public exploit reference; Remotely exploitable, no login, no user action

References

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