CVE-2026-34840 OneUptime SSO: Multi-Assertion Identity Injection via Decoupled Signature Verification

High 8.1 Published 2 Apr 2026 Updated 2 Apr 2026

Attackers can bypass SAML SSO authentication by injecting unsigned assertions, allowing unauthorized access to OneUptime accounts.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-34840?

CVE-2026-34840 is a high-severity authentication bypass vulnerability in oneuptime, published on 2 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

OneUptime is an open-source monitoring and observability platform. Prior to version 10.0.42, OneUptime's SAML SSO implementation (App/FeatureSet/Identity/Utils/SSO.ts) has decoupled signature verification and identity extraction. isSignatureValid() verifies the first <Signature> element in the XML DOM using xml-crypto, while getEmail() always reads from assertion[0] via xml2js. An attacker can prepend an unsigned assertion containing an arbitrary identity before a legitimately signed assertion, resulting in authentication bypass. This issue has been patched in version 10.0.42.

Weakness: CWE-347

Which versions are affected by CVE-2026-34840?

It affects 1 product.

Products include Hackerbay Oneuptime.

How do I fix CVE-2026-34840?

No fix has been published for CVE-2026-34840 yet. Limit exposure of the affected software until one is available.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2026-34840 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-34840 exists.

Sources

Also known as GHSA-5w5c-766x-265g.