Redirect URL matching ignores character casing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N

EPSS

• CVE-2020-15234: 0.84% estimated exploitation activity in the next 30 days; percentile 57.94 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Before version v0.34.1, the OAuth 2.0 Client's registered redirect URLs and the redirect URL provided at the OAuth2 Authorization Endpoint where compared using strings.ToLower while they should have been compared with a simple string match: 1. Registering a client with allowed redirect URL https://example.com/callback 2. Performing OAuth2 flow and requesting redirect URL https://example.com/CALLBACK 3. Instead of an error (invalid redirect URL), the browser is redirected to https://example.com/CALLBACK with a potentially successful OAuth2 response, depending on the state of the overall OAuth2 flow (the user might still deny the request for example).

Published by the source

24 May 2021, 17:00 UTC

Last modified by the source

1 Feb 2023, 05:05 UTC

Source last checked

26 Oct 2026, 14:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-grfp-q2mm-hfp6

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# Patch Next advisory brief: CVE-2020-15234

Advisory: Redirect URL matching ignores character casing
IDs: CVE-2020-15234, GHSA-grfp-q2mm-hfp6
Record: https://patchnext.com/advisories/cve-2020-15234 (revision 1, source checked 26 Oct 2026, 14:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/ory/fosite 0.34.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/ory/fosite: affected < 0.34.1; fixed in 0.34.1

## Suggested inspection (read-only)
- Go github.com/ory/fosite: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/ory/fosite.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-grfp-q2mm-hfp6 (GitHub-reviewed advisory GHSA-grfp-q2mm-hfp6 lists affected ranges: Go github.com/ory/fosite >=0 <0.34.1)

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