CVE-2026-56099Disclosure(openbsd / openbsd)

MEDIUMCVSS 5.3 · MEDIUM

Exploit discussion active in current signal (1 latest mentions)

Immediate actions

Patch openbsd openbsd systems immediately
Hunt for exploitation attempts and persistence artifacts
Increase monitoring for publicly documented tradecraft

Recommended action window: High priority (within 72h)

NVD 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.

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4.0/ 10 priority

Sources & remediation

Patch / fix

Exploit / PoC references

Vendor / third-party advisories

https://www.vulncheck.com/advisories/openbsd-mpls-do-error-kernel-stack-memory-disclosure-via-mpls-input

Weakness type (CWE)

CWE-125

Priority

MEDIUM

Exploitation

NONE

PoC

YES

Patch

AVAILABLE

Momentum

STABLE

Are you affected?

If you run products in this scope, you should treat this CVE as relevant to your environment.

openbsd

Threat summary

Public PoC and exploit tooling are both present
Patch or workaround signal is available
6 mentions across 3 observed days
Momentum state: stable

What's happening

Exploit tool or code specified in 1 signal
PoC mentioned or linked in 2 signals
Patch or workaround mentioned in 1 signal
Technical details provided in 5 signals
Disclosure: 4 classified signals
General: 1 classified signal
Peaked 1d ago at 3 mentions (2026-06-19); latest day: 1
6 total mentions across 3 days

Affected systems

Vendors

openbsd

Products

openbsd

Deep dive

Activity timeline6 mentions / 3d

Signal classification3 categories

Disclosure

466.7%

PoC

116.7%

General

116.7%

Referenced assets4 URLs

By indicator

Classification over time

Date	Total	Labels

2026-06-18	2	Disclosure2
2026-06-19	3	Disclosure2PoC1
2026-08-25	1	General1

Full discourse6 posts

Open Source Security mailing list@oss_security90d
PoC
CVE-2026-56099: OpenBSD: mpls_do_error: Remote Kernel Stack Disclosure via MPLS Label Stack Over-read https://www.openwall.com/lists/oss-security/2026/06/19/3 Python/Scapy PoC. The reply carries 17 MPLS shim headers on the wire; the 17th is the leaked kernel stack data. Fixed in -current on 2026-06-18.
Post summary
OpenBSD’s CVE‑2026‑56099 causes a kernel stack disclosure through an over‑read in MPLS handling; a Python/Scapy PoC demonstrates the leak with 17 headers, and the issue was fixed in the current branch on 2026‑06‑18.
00061773
4.7K followersView on X
/r/netsec@_r_netsec91d
Disclosure
OpenBSD MPLS kernel stack leaks remotely (CVE-2026-56099) https://pop.argus-systems.ai/advisory/adv-040.html
Post summary
An advisory has been issued for CVE-2026-56099, indicating a remote stack leakage vulnerability in the OpenBSD MPLS kernel. No PoC, exploit code, or mitigation details are disclosed.
01030757
33.6K followersView on X
Nicolas Krassas@Dinosn91d
Disclosure
OpenBSD MPLS kernel stack leaks remotely (CVE-2026-56099) https://pop.argus-systems.ai/advisory/adv-040.html
Post summary
The advisory announces a new remote stack leakage in OpenBSD’s MPLS kernel (CVE-2026-56099), but it does not provide a PoC, exploit, active exploitation evidence, or patch details.
010201.8K
159.6K followersView on X
Mehrun@mehrrun24d
General
My two cents is that this democratises AI-availability and Privacy. Doom on hardware Y is an existence proof and dies there! For fulfilling your curiosity running a glm-5.1 UD-IQ1_M on one Mac studio M3 ultra plus a iogpu sysctl made us at #byteray #CVE-2026-55706 a 27-year old bug on #OpenBSD just a few weeks after Mythos worked heavily on the same part of the its kernel! Btw, it wasn’t just an llm prompt to hunt bugs, however a bit more work on agents, pairing 1bit quant with precomputed CPG/DFG analysis yet autonomously, RAG over mcp. The setup also leads us to hundreds of advisories including: #CVE-2026-55706 #CVE-2026-71967 #CVE-2026-71968 #CVE-2026-71969 #CVE-2026-71970 #CVE-2026-71971 #CVE-2026-71972 #CVE-2026-71973 #CVE-2026-71974 #CVE-2026-74220 #CVE-2026-74221 #CVE-2026-74222 #CVE-2026-74223 #CVE-2026-74224 #CVE-2026-74225 #CVE-2026-56099 #CVE-2026-56101 #CVE-2026-56102 #CVE-2026-56103 Yet all of these are just a small use case not a benchmark so I agree with you on that part @theByteRay
Post summary
The post highlights experimental discovery of several CVEs and mentions a proof of concept, but lacks concrete technical details, exploitation code, or patch information.
00010114
267 followersView on X
Infoflowcloud@infoflowcloud91d
Disclosure
🚨*CVE* CVE-2026-56099 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 remo… https://www.cve.org/CVERecord?id=CVE-2026-56099 ----- Traducción: CVE-2026-56099 Ope… http://infoflow.cloud`
Post summary
The tweet announces a newly disclosed CVE-2026-56099 in OpenBSD, describing an out‑of‑bounds read bug in the MPLS error handling code.
0000071
82 followersView on X
CVE@CVEnew91d
Disclosure
CVE-2026-56099 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 remo… https://www.cve.org/CVERecord?id=CVE-2026-56099
Post summary
OpenBSD's CVE-2026-56099 is an out‑of‑bounds read in mpls_do_error before commit 6a23123, with no PoC, exploit, or patch mentioned.
00000284
57.6K followersView on X

CPE platform detail1 entries

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Vendor:

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Target SW:

Target HW:

1 of 1 entries

Part	Vendor	Product	Version	Target SW	Target HW
OS	openbsd	openbsd	-	-	-

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What researchers are saying

CVE-2026-56099

Nicolas Krassas[verified]@DinosnDisclosure

The advisory announces a new remote stack leakage in OpenBSD’s MPLS kernel (CVE-2026-56099), but it does not provide a PoC, exploit, active exploitation evidence, or patch details.

Mehrun[verified]@mehrrunGeneral

The post highlights experimental discovery of several CVEs and mentions a proof of concept, but lacks concrete technical details, exploitation code, or patch information.

Open Source Security mailing list@oss_securityPoC

OpenBSD’s CVE‑2026‑56099 causes a kernel stack disclosure through an over‑read in MPLS handling; a Python/Scapy PoC demonstrates the leak with 17 headers, and the issue was fixed in the current branch on 2026‑06‑18.

/r/netsec@_r_netsecDisclosure

An advisory has been issued for CVE-2026-56099, indicating a remote stack leakage vulnerability in the OpenBSD MPLS kernel. No PoC, exploit code, or mitigation details are disclosed.

Infoflowcloud@infoflowcloudDisclosure

The tweet announces a newly disclosed CVE-2026-56099 in OpenBSD, describing an out‑of‑bounds read bug in the MPLS error handling code.

CVE@CVEnewDisclosure

OpenBSD's CVE-2026-56099 is an out‑of‑bounds read in mpls_do_error before commit 6a23123, with no PoC, exploit, or patch mentioned.