# CVE-2026-42300: DevGuard: Unauthenticated identity assertion via `X-Admin-Token` header

> An unauthenticated attacker can impersonate any user, including admins, by supplying a known UUID in the X-Admin-Token header, gaining full control over organization resources.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 May 2026
- **Updated:** 13 May 2026
- **Also known as:** GHSA-2g9v-7mr5-fgjg, GO-2026-4988

## What is CVE-2026-42300?

CVE-2026-42300 is a critical authentication bypass vulnerability in l3montree-dev devguard, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

DevGuard provides vulnerability management for the full software supply chain. Prior to 1.2.2, the SessionMiddleware accepts a client-supplied X-Admin-Token HTTP request header and uses its raw string value as the authenticated userID when no Kratos session cookie is present. An unauthenticated attacker who knows or can guess a target user's Kratos identity UUID can issue requests as that user. Where the target user is an organisation admin or owner, this gives the attacker full control over that organisation's DevGuard resources. This vulnerability is fixed in 1.2.2.

Weakness: CWE-288 (Authentication Bypass Using an Alternate Path or Channel)

## Which versions are affected by CVE-2026-42300?

3 open source packages ship an affected version, including github.com/l3montree-dev/devguard.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/l3montree-dev/devguard` | Go | All versions | 1.2.2 |
| `github.com/l3montree-dev/devguard` | Go | All versions | 1.2.2 |
| `github.com/l3montree-dev/devguard` | Go | All versions | 1.2.2 |

## How do I fix CVE-2026-42300?

Upgrade github.com/l3montree-dev/devguard to 1.2.2 or later.

## Is CVE-2026-42300 being exploited?

There is no known exploitation of CVE-2026-42300 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42300 and fix it if it is affected.

What it is: CVE-2026-42300 is a critical authentication bypass vulnerability in l3montree-dev devguard, published on 12 May 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-2026-42300 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/l3montree-dev/devguard (Go): affected all versions; fixed in 1.2.2
- github.com/l3montree-dev/devguard (Go): affected all versions; fixed in 1.2.2
- github.com/l3montree-dev/devguard (Go): affected all versions; fixed in 1.2.2

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-2026-42300/ (Markdown: https://insights.sbomify.com/CVE-2026-42300/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42300
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42300
- OSV: https://osv.dev/vulnerability/CVE-2026-42300

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42300/
Summaries are generated and may contain mistakes; the official description above is the record.