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

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

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Apr 2026
- **Updated:** 2 Apr 2026
- **Also known as:** GHSA-5w5c-766x-265g

## 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 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-34840?

It affects 1 product.


Products: 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.

## Is CVE-2026-34840 being exploited?

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

## Other vulnerabilities in oneuptime

- [CVE-2026-33396](https://insights.sbomify.com/CVE-2026-33396/): Code injection in oneuptime (critical 10.0)
- [CVE-2026-32306](https://insights.sbomify.com/CVE-2026-32306/): OneUptime ClickHouse SQL Injection via Aggregate Query Parameters (critical 10.0)
- [CVE-2026-30956](https://insights.sbomify.com/CVE-2026-30956/): OneUptime has authorization bypass via client‑controlled is-multi-tenant-query header (critical 10.0)
- [CVE-2026-30957](https://insights.sbomify.com/CVE-2026-30957/): OneUptime Synthetic Monitor RCE via exposed Playwright browser object (critical 10.0)
- [CVE-2026-30887](https://insights.sbomify.com/CVE-2026-30887/): OneUptime Affected by Unsandboxed Code Execution in Probe Allows Any Project Member to Achieve RCE (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34840 and fix it if it is affected.

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

Affected product: oneuptime. 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-2026-34840/ (Markdown: https://insights.sbomify.com/CVE-2026-34840/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34840
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34840
- OSV: https://osv.dev/vulnerability/CVE-2026-34840

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34840/
Summaries are generated and may contain mistakes; the official description above is the record.