Vulnerability in mesop (CVE-2026-93421)
Summary
Vulnerability in mesop (CVE-2026-93421). Risk of unauthorized operations or information disclosure. Exploitable via POST /__csp__. Mitigation: upgrade to 1.3.4 or later.
Original description
The description as published by the source.
Summary
The /__csp__ endpoint accepts unauthenticated JSON reports and logs user-controlled values directly to stdout using print() without escaping control characters.
A remote attacker can include ANSI/VT100 escape sequences in fields such as blocked-uri or document-uri. When the logs are viewed in an ANSI-capable terminal, these sequences can manipulate the displayed output (e.g., clear the screen, hide text, or inject misleading messages), affecting the integrity of operator-facing logs.
Details
The CSP reporting endpoint accepts arbitrary JSON and prints several request fields directly:
mesop/server/static_file_serving.py
@app.route(prefix_base_url("/__csp__"), methods=["POST"])
def csp_report():
report = request.get_json(force=True)
document_uri = report["csp-report"]["document-uri"]
blocked_uri = report["csp-report"]["blocked-uri"]
violated_directive = report["csp-report"]["violated-directive"]
print(f"... Blocked URL: {blocked_uri} ...")
Since these values are written to stdout without sanitization, ANSI escape sequences supplied by a remote client are preserved and interpreted by ANSI-compatible terminals.
PoC
Send the following request:
POST /__csp__
Content-Type: application/json
{
"csp-report": {
"document-uri": "https://victim.example",
"blocked-uri": "\u001b[2J\u001b[H\u001b[32m*** SECURITY OK - No CSP violations found ***\u001b[0m\n\u001b[8mhttps://evil.example",
"violated-d…
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-2026-93421 has been found in mesop.
Attackers can target a specific entry point like POST /__csp__ over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade mesop to 1.3.4 or later.
If unsure, ask your IT team or search "mesop CVE-2026-93421" on the vendor's site.
CVE-2026-93421 (mesop) — CWE-117
Attack surface: POST /csp / pyte
Patched: 1.3.4 — 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.
A vulnerability (CWE-117) exists in mesop. Attackers reach the vulnerable code path via POST /__csp__.
Check the vendor advisory for the affected versions of mesop. Attack surface: POST /csp / pyte.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 1.3.4.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual POST /__csp__ requests with malformed payloads or SQL meta-characters. Run grep -r 'mesop' . 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 'mesop' . | 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
mesop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 'POST /__csp__' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
POST /__csp__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 mesop to 1.3.4ステージング環境で 1.3.4 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。
-
4Post-deployment verification verify
Replay attack against POST /__csp__ 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
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com
- web github.com