Summary
Concourse login flow has an open redirect issue
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.
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.
Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-49826? CVE-2026-49826 is a low-severity open redirect vulnerability in github.com/concourse/concourse (go), affecting versions < 1.6.1-0.20260526150512-ac60be5f0435. It is fixed in 1.6.1-0.20260526150512-ac60be5f0435. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
- Which versions of github.com/concourse/concourse are affected by CVE-2026-49826? github.com/concourse/concourse (go) versions < 1.6.1-0.20260526150512-ac60be5f0435 is affected.
- Is there a fix for CVE-2026-49826? Yes. CVE-2026-49826 is fixed in 1.6.1-0.20260526150512-ac60be5f0435. Upgrade to this version or later.
- Is CVE-2026-49826 exploitable, and should I be worried? Whether CVE-2026-49826 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-49826 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-49826? Upgrade
github.com/concourse/concourseto 1.6.1-0.20260526150512-ac60be5f0435 or later.