CVE-2026-49826 — concourse
Fix: concourse/concourse@ac60be5CVE-2026-49826 is a Open Redirect vulnerability in github.com/concourse/concourse. A fix is available for github.com/concourse/concourse — see the affected versions and patch details below.
Concourse login flow has an open redirect issue
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-49826.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
github.com/concourse/concourseReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
An attacker is able to craft and send a user a URL that will redirect the user from the Concourse web server to any other site. This could be used in a phishing attack to steal user's credentials.
Patches
This has been fixed in 8.2.3
Workarounds
None.
Exploit
Vulnerable code was in: https://github.com/concourse/concourse/blob/ea7b812e3a88fdd070f0faece874e8a2d4fbb31c/skymarshal/skyserver/skyserver.go#L162-L170
The issue stems from the underlying processing logic of Go's url package. Normally, ParseRequestURI() will eventually reach an internal url.setPath() function, where the URL will be decoded. However, if RawPath is not empty and validEncoded(RawPath) is true, and the decoded result equals Path, then return RawPath as is; otherwise, escape Path again, i.e., decode it again.
In other words, if the URL contains dangerous characters that should be escaped, such as backslashes (\), then an extra decoding step will be performed. Therefore, /%2Fexample.com will be parsed as //example.com.
On vulnerable versions of Concourse, add /sky/login?redirect_uri=/%252Fexample.com/\ to your Concourse external URL, login as usual, and you should be redirected to example.com instead of your Concourse web server. The redirect happens after the login flow completes. No credentials are leaked.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/concourse/concourse | all versions | 1.6.1-0.20260526150512-ac60be5f0435go get github.com/concourse/concourse@v1.6.1-0.20260526150512-ac60be5f0435 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/concourse/concourse, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/concourse/concourse to 1.6.1-0.20260526150512-ac60be5f0435 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49826 is resolved across your whole dependency graph.
Workarounds
Stop reflecting attacker-controlled destinations: resolve every redirect target against an allowlist of paths or hosts you own, prefer a server-side key over a full URL in the request, and reject absolute URLs entirely where the flow only ever needs a relative one.
Frequently Asked Questions
Is CVE-2026-49826 in your dependencies?
Find it across Go, including transitive dependencies.