How severe is GHSA-8w27-c4vc-88q9?

No CVSS score has been assigned to GHSA-8w27-c4vc-88q9 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-8w27-c4vc-88q9?

GHSA-8w27-c4vc-88q9 affects the following packages: github.com/concourse/concourse (Go). Ecosystems affected: Go.

How do I fix GHSA-8w27-c4vc-88q9?

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 GHSA-8w27-c4vc-88q9 is resolved across your whole dependency graph.

How do I detect GHSA-8w27-c4vc-88q9 in my Go dependencies?

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.

How do I mitigate GHSA-8w27-c4vc-88q9 if there is no patch (or I can't update yet)?

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.

Is GHSA-8w27-c4vc-88q9 actively exploited in the wild?

No public exploit code has been indexed for GHSA-8w27-c4vc-88q9 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-8w27-c4vc-88q9?

GHSA-8w27-c4vc-88q9 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 44th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-8w27-c4vc-88q9?

GHSA-8w27-c4vc-88q9 is classified as Open Redirect (CWE-601). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-8w27-c4vc-88q9 published, and has it been updated?

GHSA-8w27-c4vc-88q9 was published on July 1, 2026 and was last updated on August 19, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

Concourse login flow has an open redirect issueGHSA-8w27-c4vc-88q9

Fix: concourse/concourse@ac60be5

GHSA-8w27-c4vc-88q9 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.

Also known asBIT-concourse-2026-49826CVE-2026-49826GO-2026-5866

Published

Jul 1, 2026

Updated

Aug 19, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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 GHSA-8w27-c4vc-88q9.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs44th percentile — riskier than 44% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐹github.com/concourse/concourse

Real-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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/concourse/concourse`	all versions	1.6.1-0.20260526150512-ac60be5f0435`go get github.com/concourse/concourse@v1.6.1-0.20260526150512-ac60be5f0435`

Detection & mitigation playbook

Open-source dependency

Detect
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 GHSA-8w27-c4vc-88q9 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

### 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()`

O3 Security · Impact-Aware SCA

Is GHSA-8w27-c4vc-88q9 in your dependencies?

Find it across Go, including transitive dependencies.

Scan my dependencies How O3 SCA works