OAuth2 Redirect URL validity does not respect query parameters and character casing for loopback addresses

Exploitation

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

CVSS

5.5 · CVSS:3.0/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N/E:P/RL:O/RC:C

EPSS

• CVE-2020-15233: 0.80% estimated exploitation activity in the next 30 days; percentile 56.61 (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 fosite#400 (released as v0.30.2) introduced a new feature for handling redirect URLs pointing to loopback interfaces (rfc8252#section-7.3). As part of that change new behavior was introduced which failed to respect the redirect URL's (only for loopback interfaces!) query parameters 1. Registering a client with allowed redirect URL http://127.0.0.1/callback 2. Performing OAuth2 flow and requesting redirect URL http://127.0.0.1/callback?bar=foo 3. Instead of an error, the browser is redirected to http://127.0.0.1/callback?bar=foo with a potentially successful OAuth2 response. as well as the host parameter (as long as the host is a loopback interface): 1. Registering a client with allowed redirect URL https://example.com/callback 2. Performing OAuth2 flow and requesting redirect URL http://127.0.0.1/callback 3. Instead of an error, the browser is redirected to http://127.0.0.1/callback with a potentially successful OAuth2 response. These bugs are only applicable in scenarios…

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-rfq3-w54c-f9q5

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# Patch Next advisory brief: CVE-2020-15233

Advisory: OAuth2 Redirect URL validity does not respect query parameters and character casing for loopback addresses
IDs: CVE-2020-15233, GHSA-rfq3-w54c-f9q5
Record: https://patchnext.com/advisories/cve-2020-15233 (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 5.5)
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 >= 0.30.3, < 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-rfq3-w54c-f9q5 (GitHub-reviewed advisory GHSA-rfq3-w54c-f9q5 lists affected ranges: Go github.com/ory/fosite >=0.30.3 <0.34.1)

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