# CVE-2026-5123: osrg GoBGP bgp.go DecodeFromBytes off-by-one

> An off-by-one error in GoBGP's DecodeFromBytes function allows remote attackers to cause a denial of service via complex manipulation.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 30 Mar 2026
- **Updated:** 1 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-5123, GHSA-m763-9mqf-95rq, UBUNTU-CVE-2026-5123

## What is CVE-2026-5123?

CVE-2026-5123 is a medium-severity vulnerability in osrg GoBGP, published on 30 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A weakness has been identified in osrg GoBGP up to 4.3.0. This impacts the function DecodeFromBytes of the file pkg/packet/bgp/bgp.go. Executing a manipulation of the argument data[1] can lead to off-by-one. The attack may be launched remotely. Attacks of this nature are highly complex. The exploitability is said to be difficult. This patch is called 67c059413470df64bc20801c46f64058e88f800f. A patch should be applied to remediate this issue.

Weakness: CWE-193 (Off-by-one Error), CWE-189

## Which versions are affected by CVE-2026-5123?

It affects 1 product.


Products: Osrg Gobgp.

## How do I fix CVE-2026-5123?

Apply the vendor's patch.

## Is CVE-2026-5123 being exploited?

There is no known exploitation of CVE-2026-5123 in the wild and no public exploit code.

## Other vulnerabilities in osrg GoBGP

- [CVE-2025-43971](https://insights.sbomify.com/CVE-2025-43971/): GoBGP panics due to a zero value for softwareVersionLen (high 8.6)
- [CVE-2026-41642](https://insights.sbomify.com/CVE-2026-41642/): GoBGP: Remote Denial of Service (Panic) via Malformed Well-known Path Attribute (high 7.5)
- [CVE-2026-41643](https://insights.sbomify.com/CVE-2026-41643/): GoBGP: Remote Denial of Service (Panic) in UpdatePathAttrs4ByteAs via Malformed BGP UPDATE (high 7.5)
- [CVE-2026-42285](https://insights.sbomify.com/CVE-2026-42285/): GoBGP: Panic in AdjRib.Update via malformed BGP Update message (Nil Pointer Dereference) (high 7.5)
- [CVE-2026-37461](https://insights.sbomify.com/CVE-2026-37461/): GoBGP has an out-of-bounds read in the ParseIP6Extended function (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-5123 and fix it if it is affected.

What it is: CVE-2026-5123 is a medium-severity vulnerability in osrg GoBGP, published on 30 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-5123 in the wild and no public exploit code.

Affected product: osrg GoBGP. 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-2026-5123/ (Markdown: https://insights.sbomify.com/CVE-2026-5123/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-5123
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-5123
- OSV: https://osv.dev/vulnerability/CVE-2026-5123

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-5123/
Summaries are generated and may contain mistakes; the official description above is the record.