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GHSA-8w27-c4vc-88q9
No affected components available
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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights.
No exploitation activity has been observed at this time. Continue routine monitoring.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
- CVE-2026-49826Alias
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