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CVE-2021-41270

Vulnerability in symfony/serializer (CVE-2021-41270)

Summary

Vulnerability in symfony/serializer (CVE-2021-41270). Confidential information can be exposed externally. Exploitable via csv_escape_formulas. Mitigation: upgrade to 4.4.35 or later.

Original description

The description as published by the source.

Symfony/Serializer handles serializing and deserializing data structures for Symfony, a PHP framework for web and console applications and a set of reusable PHP components. Symfony versions 4.1.0 before 4.4.35 and versions 5.0.0 before 5.3.12 are vulnerable to CSV injection, also known as formula injection. In Symfony 4.1, maintainers added the opt-in csv_escape_formulas option in the CsvEncoder, to prefix all cells starting with =, +, - or @ with a tab \t. Since then, OWASP added 2 chars in that list: Tab (0x09) and Carriage return (0x0D). This makes the previous prefix char (Tab \t) part of the vulnerable characters, and OWASP suggests using the single quote ' for prefixing the value. Starting with versions 4.4.34 and 5.3.12, Symfony now follows the OWASP recommendations and uses the single quote ' to prefix formulas and add the prefix to cells starting by \t, \r as well as =, +, - and @.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

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-2021-41270 has been found in symfony/serializer.
Attackers can target a specific entry point like csv_escape_formulas over the network to misuse the product.
Confidential information can be exposed externally.
What to do: upgrade symfony/serializer to 4.4.35 or later.
If unsure, ask your IT team or search "symfony/serializer CVE-2021-41270" on the vendor's site.

CVE-2021-41270 (symfony/serializer) — CWE-1236
Attack vector: remote (network-reachable) / no user interaction
Attack surface: csv_escape_formulas / CsvEncoder
Patched: 4.4.35 — 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-1236) exists in symfony/serializer. Attackers reach the vulnerable code path via csv_escape_formulas.

📍 Affected scope

Check the vendor advisory for the affected versions of symfony/serializer. Attack surface: csv_escape_formulas / CsvEncoder.

🔥 Severity

Severity: ?. Confidential information can be exposed externally.

🔧 How to fix

Update to 4.4.35.

🛡️ 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 'symfony/serializer' . 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 'symfony/serializer' . | 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 symfony/serializer 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 symfony/serializer to 4.4.35

    ステージング環境で 4.4.35 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

Packagist symfony/serializer
[{"type":"ECOSYSTEM","events":[{"introduced":"4.1.0"},{"fixed":"4.4.35"}]}]
Packagist symfony/symfony
[{"type":"ECOSYSTEM","events":[{"introduced":"5.0.0"},{"fixed":"5.3.12"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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