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CVE-2026-34830 medium CVSS 5.9

Vulnerability in rack (CVE-2026-34830)

Summary

Vulnerability in rack (CVE-2026-34830). Confidential information can be exposed externally. Exploitable via internal. Mitigation: upgrade to 3.2.6 or later.

Original description

The description as published by the source.

Summary

Rack::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and control the generated X-Accel-Redirect response header.

In deployments using Rack::Sendfile with x-accel-redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal locations.

Details

Rack::Sendfile#map_accel_path processes header-supplied mappings using logic equivalent to:

mapping.split(',').map(&:strip).each do |m|
  internal, external = m.split('=', 2).map(&:strip)
  new_path = path.sub(/\A#{internal}/i, external)
  return new_path unless path == new_path
end

Here, internal comes from the HTTP_X_ACCEL_MAPPING request header and is inserted directly into a regular expression without escaping. This gives the header value regex semantics rather than treating it as a literal prefix.

As a result, an attacker can supply metacharacters such as .* or capture groups to alter how the path substitution is performed. For example, a mapping such as:

X-Accel-Mapping: .*=/protected/secret.txt

causes the entire source path to match and rewrites the redirect target to a clean attacker-chosen internal path.

This differs from the documented behavior of the header-based mapping…

Source: GitHub Security Advisories (Global) 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-2026-34830 has been found in rack.
Attackers can target a specific entry point like internal over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 5.9/10.
What to do: upgrade rack to 3.2.6 or later.
If unsure, ask your IT team or search "rack CVE-2026-34830" on the vendor's site.

CVE-2026-34830 (rack) — CWE-625 / CVSS v3 5.9
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: internal / HTTP_X_ACCEL_MAPPING
Patched: 3.2.6 — 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.

❓ What is the problem

A vulnerability (CWE-625) exists in rack. Attackers reach the vulnerable code path via internal without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of rack. Attack surface: internal / HTTP_X_ACCEL_MAPPING.

🔥 Severity

Severity: Medium (CVSS 5.9/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 3.2.6.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'rack' . 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

  1. 1
    Identify exposure identify 
    grep -r 'rack' . | 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 rack を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade rack to 3.2.6

    ステージング環境で 3.2.6 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を含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    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。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

rubygems rack
[{"type":"ECOSYSTEM","events":[{"introduced":"3.2.0"},{"fixed":"3.2.6"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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