CVE-2026-42882 oxyno-zeta/s3-proxy: Security Issues in Resource Path Matching
Unauthenticated attackers can bypass authentication to read, write, or delete S3 objects due to path matching inconsistencies.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42882?
CVE-2026-42882 is a critical authentication bypass vulnerability in oxyno-zeta s3-proxy, published on 11 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-42882?
3 open source packages ship an affected version, including github.com/oxyno-zeta/s3-proxy.
| Package | Affected | Fixed in |
|---|---|---|
github.com/oxyno-zeta/s3-proxy Go | All versions | 0.0.0-20260424211602-1320e4abd46a |
github.com/oxyno-zeta/s3-proxy Go | All versions | 0.0.0-20260424211602-1320e4abd46a |
github.com/oxyno-zeta/s3-proxy Go | All versions | 0.0.0-20260424211602-1320e4abd46a |
How do I fix CVE-2026-42882?
Upgrade github.com/oxyno-zeta/s3-proxy to 0.0.0-20260424211602-1320e4abd46a or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-42882 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42882 exists.
Sources
Also known as GHSA-rfgq-wgg8-662p, GO-2026-5616.