Path Traversal in github.com/oxyno-zeta/s3-proxy (CVE-2026-42882)
Summary
Path traversal in github.com/oxyno-zeta/s3-proxy (CVE-2026-42882). Confidential information can be exposed externally. Exploitable via PUT /upload/foo/drafts/../restricted/. Mitigation: upgrade to 0.0.0-20260424211602-1320e4abd46a or later.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-42882 has been found in github.com/oxyno-zeta/s3-proxy.
Attackers can target a specific entry point like PUT /upload/foo/drafts/../restricted/ over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.4/10.
What to do: upgrade github.com/oxyno-zeta/s3-proxy to 0.0.0-20260424211602-1320e4abd46a or later.
If unsure, ask your IT team or search "github.com/oxyno-zeta/s3-proxy CVE-2026-42882" on the vendor's site.
CVE-2026-42882 (github.com/oxyno-zeta/s3-proxy) — CWE-22 / CVSS v3 9.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: PUT /upload/foo/drafts/../restricted/ / PUT /upload/foo / PUT /upload/foo/drafts/ / PUT /open/../restricted/secret.json
Patched: 0.0.0-20260424211602-1320e4abd46a — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Path traversal (CWE-22) exists in github.com/oxyno-zeta/s3-proxy. Attackers reach the vulnerable code path via PUT /upload/foo/drafts/../restricted/ without authentication.
Check the vendor advisory for the affected versions of github.com/oxyno-zeta/s3-proxy. Attack surface: PUT /upload/foo/drafts/../restricted/ / PUT /upload/foo / PUT /upload/foo/drafts/ / PUT /open/../restricted/secret.json.
Severity: Critical (CVSS 9.4/10). Confidential information can be exposed externally.
Update to 0.0.0-20260424211602-1320e4abd46a.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual PUT /upload/foo/drafts/../restricted/ requests with malformed payloads or SQL meta-characters. Run grep -r 'github.com/oxyno-zeta/s3-proxy' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/oxyno-zeta/s3-proxy' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/oxyno-zeta/s3-proxyを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'PUT /upload/foo/drafts/../restricted/' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
PUT /upload/foo/drafts/../restricted/への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Apply patch patch
Upgrade github.com/oxyno-zeta/s3-proxy to 0.0.0-20260424211602-1320e4abd46aステージング環境で 0.0.0-20260424211602-1320e4abd46a に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスと、Step 2 で見つけた異常検知の続報チェックを含めること。
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4Post-deployment verification verify
Replay attack against PUT /upload/foo/drafts/../restricted/ on staging to confirm patch closes the vectorパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- patch github.com
- patch github.com
- web github.com