Yamcs has Unauthenticated Directory Traversal

Answer in brief

CVE-2026-55552 records a High severity (CVSS 7.5) vulnerability in Yamcs has Unauthenticated Directory Traversal. The current sources do not mark it as known exploited. The current feed maps org.yamcs:yamcs-core (maven). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 28, 2026Updated Aug 28, 2026Source checked Aug 28, 2026First seen by HOL Aug 28, 2026Material review Aug 28, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.5
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps org.yamcs:yamcs-core (maven). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
org.yamcs:yamcs-coremaven	<5.11.13	5.12.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for org.yamcs:yamcs-core.
Review the reported fix. Update org.yamcs:yamcs-core to 5.12.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 28, 2026
Evidence: source:ghsa:source_dates:source-dates:record
Source modified
Aug 28, 2026
Evidence: source:ghsa:source_dates:source-dates:record
First seen by HOL
Aug 28, 2026

Sources and claim methodology

Upstream source description

### Attack type:  Unauthenticated remote  ### Impact: Attackers can access any system files from the underlying host. ### Affected components: HttpRequestHandler.java, StaticFileHandler.java An Unauthenticated Directory Traversal vulnerability exists in Yamcs <=5.8.6, allowing anyone to access any file on the underlying operating system. This allows unauthenticated attackers to download sensitive files and data. <img width="2170" height="1289" alt="image" src="https://github.com/user-attachments/assets/8d426da1-5351-4240-a290-8d858be61312" /> ## Steps to Reproduce: 1. Start Yamcs and login as a user 2. Paste the following URL in the browser and press enter: ``` http://localhost:8090//etc/passwd ``` 3. The `/etc/passwd` file will be downloaded. ## Acknowledgements This vulnerability was discovered by Abderrahim Dahmani while solving a STARPWN 2025 CTF challenge at DEFCON 33 offered by VisionSpace Technologies.

Quoted source text, attributed separately from HOL analysis.