# CVE-2026-49943: Memory corruption in BIRD

> A remote BGP peer can crash the BIRD daemon via a stack buffer overflow in AS_PATH matching when Extended Messages are enabled.

- **Severity:** Medium 6.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Jun 2026
- **Updated:** 2 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-49943, GHSA-64c8-8qx9-25r7, UBUNTU-CVE-2026-49943

## What is CVE-2026-49943?

CVE-2026-49943 is a medium-severity memory corruption vulnerability in NIC BIRD, published on 2 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

CZ.NIC BIRD Internet Routing Daemon through 2.19.0 contains a stack-based buffer overflow in the BGP AS_PATH mask matching implementation in nest/a-path.c. The as_path_match() function uses a fixed-size stack array of 2048 + 1 pm_pos entries, while parse_path() expands AS_PATH segments from a received BGP UPDATE without enforcing a corresponding capacity limit. When RFC 8654 BGP Extended Messages are enabled and a BIRD filter evaluates an AS path mask expression such as "bgp_path ~ [= ... =]", an established BGP peer can send a long AS_PATH containing more than 2048 expanded ASNs. This causes parse_path()/as_path_match() to write beyond the fixed stack buffer, resulting in a crash of the daemon. NOTE: reportedly, the Supplier's position is that a fix is not being prioritized because all network operators should already be rejecting routes with unusually long attributes.

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-49943?


## How do I fix CVE-2026-49943?

No fix has been published for CVE-2026-49943 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-49943 being exploited?

There is no known exploitation of CVE-2026-49943 in the wild and no public exploit code.

Public exploit code:

- PoC of CVE-2026-49943 (github_poc): https://github.com/cxwx/CVE-2026-49943-PoC

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49943 and fix it if it is affected.

What it is: CVE-2026-49943 is a medium-severity memory corruption vulnerability in NIC BIRD, published on 2 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-49943 in the wild and no public exploit code.

Affected product: NIC BIRD. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-49943/ (Markdown: https://insights.sbomify.com/CVE-2026-49943/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49943
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49943
- OSV: https://osv.dev/vulnerability/CVE-2026-49943

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49943/
Summaries are generated and may contain mistakes; the official description above is the record.