S3-Proxy has Security Issues in its Resource Path Matching Implementation

Exploitation

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

CVSS

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

EPSS

• CVE-2026-42882: 0.55% estimated exploitation activity in the next 30 days; percentile 46.32 (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.

Background The original concern is functional: a resource pattern should treat a percent-encoded segment like some%2Fvalue as a single opaque token rather than splitting it into two path segments at the decoded /. Investigation into why %2F was being decoded and how routes matched against the result surfaced three related security issues, documented below. Rather than landing a fix directly, the problem space warrants discussion first. Different fixes carry different compliance and compatibility tradeoffs, and every viable option is a breaking change in some form. Aligning on a direction before committing to an implementation is the safer path. Root cause: two different path representations Go's net/http decodes percent-encoded characters when it parses an incoming URL: %2F becomes / in r.URL.Path, while the original encoded form is preserved in r.URL.RawPath. Two different parts of s3-proxy use different fields: - The auth middleware calls r.URL.RequestURI(), which returns the…

Published by the source

5 May 2026, 18:52 UTC

Last modified by the source

13 May 2026, 14:19 UTC

Source last checked

26 Oct 2026, 15:20 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-rfgq-wgg8-662p

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# Patch Next advisory brief: CVE-2026-42882

Advisory: S3-Proxy has Security Issues in its Resource Path Matching Implementation
IDs: CVE-2026-42882, GHSA-rfgq-wgg8-662p
Record: https://patchnext.com/advisories/cve-2026-42882 (revision 1, source checked 26 Oct 2026, 15:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/oxyno-zeta/s3-proxy 0.0.0-20260424211602-1320e4abd46a. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/oxyno-zeta/s3-proxy: affected < 0.0.0-20260424211602-1320e4abd46a; fixed in 0.0.0-20260424211602-1320e4abd46a

## Suggested inspection (read-only)
- Go github.com/oxyno-zeta/s3-proxy: 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/oxyno-zeta/s3-proxy.
- 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-rfgq-wgg8-662p (GitHub-reviewed advisory GHSA-rfgq-wgg8-662p lists affected ranges: Go github.com/oxyno-zeta/s3-proxy >=0 <0.0.0-20260424211602-1320e4abd46a)

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