---
title: "CVE-2026-42882: S3-Proxy has Security Issues in its Resource Path Matching Implementation"
url: https://erroneo.us/security/cve/CVE-2026-42882/
description: "CVE-2026-42882 (github.com/oxyno-zeta/s3-proxy (Go)): oxyno-zeta/s3-proxy is an aws s3 proxy written in go. Prior to 5.0.0, s3-proxy contains an…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-11
date_modified: 2026-05-13
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-42882"
kev: false
cvss: 9.4
epss: 0.00719
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-42882: S3-Proxy has Security Issues in its Resource Path Matching Implementation

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.7% , percentile 53: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 53% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes github.com/oxyno-zeta/s3-proxy (Go) < 0.0.0-20260424211602-1320e4abd46a, fixed in 0.0.0-20260424211602-1320e4abd46a . Check your lockfile, including transitive dependencies.

## What it is

oxyno-zeta/s3-proxy is an aws s3 proxy written in go. Prior to 5.0.0, s3-proxy contains an authentication bypass caused by inconsistent URL path interpretation between the authentication middleware and the bucket handler. The authentication middleware evaluates resource path patterns against the percent-encoded request URI (r.URL.RequestURI()), while the bucket handler constructs S3 object keys from the decoded path (r.URL.Path). This mismatch, combined with the glob library being invoked without a path separator (causing to match across / boundaries), allows unauthenticated attackers to write to, read from, or delete objects in protected S3 namespaces. Exploitation is possible via three techniques: (1) using patterns that match across path separators to reach protected routes via path traversal (e.g., /open/foo/drafts/../restricted/), (2) using percent-encoded slashes (%2F) to collapse multiple path segments into a single token at the auth layer while the decoded form resolves to a protected namespace at the storage layer, and (3) using dot-dot segments (../) under prefix patterns, where the raw path matches an open route while Go's URL parser resolves the traversal to a protected path before the bucket handler runs. An unauthenticated attacker with network access can perform unauthorized PUT, GET, or DELETE operations on objects in authentication-protected S3 namespaces. This vulnerability is fixed in 5.0.0.

## Affected packages

- Go `github.com/oxyno-zeta/s3-proxy` < 0.0.0-20260424211602-1320e4abd46a → fixed: 0.0.0-20260424211602-1320e4abd46a

## Affected products (CVE record)

- oxyno-zeta s3-proxy: < 5.0.0

## Severity

- GitHub_M CVSS 3.1: 9.4 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L`
- GitHub CVSS 3.1: 9.4 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.72% probability of exploitation activity in the next 30 days; percentile 53.

## Sources

- [GitHub Advisory GHSA-rfgq-wgg8-662p](https://github.com/advisories/GHSA-rfgq-wgg8-662p)
- [CVE.org record CVE-2026-42882](https://www.cve.org/CVERecord?id=CVE-2026-42882)
- [NVD entry CVE-2026-42882](https://nvd.nist.gov/vuln/detail/CVE-2026-42882)
- [github.com](https://github.com/oxyno-zeta/s3-proxy/security/advisories/GHSA-rfgq-wgg8-662p)
- [github.com](https://github.com/oxyno-zeta/s3-proxy/commit/1320e4abd46ad18c2851fedde50dbb79df8b7a51)
- [github.com](https://github.com/oxyno-zeta/s3-proxy/commit/af5ff57d8c6022459495b8fb50130073bca7b48a)

---
Source page: https://erroneo.us/security/cve/CVE-2026-42882/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt