# 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. - **Severity:** Critical 9.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 11 May 2026 - **Updated:** 13 May 2026 - **Also known as:** GHSA-rfgq-wgg8-662p, GO-2026-5616 ## 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. Weakness: CWE-863 (Incorrect Authorization), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) ## Which versions are affected by CVE-2026-42882? 3 open source packages ship an affected version, including github.com/oxyno-zeta/s3-proxy. | Package | Ecosystem | 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. ## Is CVE-2026-42882 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42882 exists. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-42882 and fix it if it is affected. What it is: 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. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42882 exists. Affected packages and fixed versions: - github.com/oxyno-zeta/s3-proxy (Go): affected all versions; fixed in 0.0.0-20260424211602-1320e4abd46a - github.com/oxyno-zeta/s3-proxy (Go): affected all versions; fixed in 0.0.0-20260424211602-1320e4abd46a - github.com/oxyno-zeta/s3-proxy (Go): affected all versions; fixed in 0.0.0-20260424211602-1320e4abd46a Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-42882/ (Markdown: https://insights.sbomify.com/CVE-2026-42882/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42882 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42882 - OSV: https://osv.dev/vulnerability/CVE-2026-42882 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-42882/ Summaries are generated and may contain mistakes; the official description above is the record.