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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-42300?
3 open source packages ship an affected version, including github.com/l3montree-dev/devguard.
| Package | 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.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-42300 being exploited?
There is no known exploitation of CVE-2026-42300 in the wild and no public exploit code.
Sources
Also known as GHSA-2g9v-7mr5-fgjg, GO-2026-4988.