# CVE-2026-117553: Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning


- **Severity:** High 7.7 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 27 Oct 2026
- **Updated:** 27 Oct 2026
- **Also known as:** GHSA-r8f2-fxjr-gx5r, GHSA-rpv9-qp4c-g469

## What is CVE-2026-117553?

CVE-2026-117553 is a high-severity vulnerability in Umbraco-CMS, published on 27 Oct 2026. 

### Official description

Umbraco CMS before 17.7.2 and 18.2.2 contains an authentication bypass vulnerability that allows unauthenticated attackers to register attacker-controlled OAuth redirect URIs by poisoning the Host header. Attackers send signed-in users authorization links using response_mode=form_post to capture codes, then redeem them via HTTP Basic client credentials to hijack back-office sessions and execute code through Razor templates.

Weakness: CWE-601 (URL Redirection to Untrusted Site)

## Which versions are affected by CVE-2026-117553?


## How do I fix CVE-2026-117553?

No fix has been published for CVE-2026-117553 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-117553 being exploited?

There is no known exploitation of CVE-2026-117553 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-117553 and fix it if it is affected.

What it is: CVE-2026-117553 is a high-severity vulnerability in Umbraco-CMS, published on 27 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-117553 in the wild and no public exploit code.

Affected product: Umbraco-CMS. 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-2026-117553/ (Markdown: https://insights.sbomify.com/CVE-2026-117553/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-117553
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-117553
- OSV: https://osv.dev/vulnerability/CVE-2026-117553

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-117553/
Summaries are generated and may contain mistakes; the official description above is the record.