CVE-2021-41270: Symfony/serializer CSV Injection Vulnerability

MODERATE
Advisory Identifier: GHSA-2xhg-w2g5-w95x
CVSS 6.5
CWE-1236
Published
Advisory Summary

CVE-2021-41270 is a MODERATE (CVSS 6.5) csv injection vulnerability (CWE-1236: Improper Neutralization of Formula Elements in a CSV File) affecting Symfony/serializer libraries in the Packagist ecosystem. The issue involves csv injection in symfony/serializer. Remediation is available by upgrading affected packages to version 5.3.12, 4.4.35.

CVE-2021-41270 at a Glance

CVE Identifier CVE-2021-41270
GHSA Identifier GHSA-2xhg-w2g5-w95x
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-1236: Improper Neutralization of Formula Elements in a CSV File
Affected Product Symfony/serializer
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2021-41270

To remediate this vulnerability, upgrade all affected Symfony/serializer dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

symfony/serializer fixed: 5.3.12
Upgrade symfony/serializer to 5.3.12
symfony/serializer fixed: 4.4.35
Upgrade symfony/serializer to 4.4.35
symfony/symfony fixed: 4.4.35
Upgrade symfony/symfony to 4.4.35
symfony/symfony fixed: 5.3.12
Upgrade symfony/symfony to 5.3.12
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

inspect dependencies for symfony/serializer

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-41270, inspect your project dependencies for Symfony/serializer:

inspect dependencies for symfony/serializer

Analyze the terminal output to locate any version of Symfony/serializer in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 5.3.12), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1236: Improper Neutralization of Formula Elements in a CSV File, where the product saves user-provided information into a comma-separated value (csv) file, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as a command when the file is opened by a spreadsheet product. In Symfony/serializer, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Description ----------- CSV Injection, also known as Formula Injection, occurs when websites embed untrusted input inside CSV files. When a spreadsheet program opens a CSV, any cell starting with `=` is interpreted by the software as a formula and could be abused by an attacker. In Symfony 4.1, we've added the opt-in `csv_escape_formulas` option in `CsvEncoder`, to prefix all cells starting by `=`, `+`, `-` or `@` by a tab `\t`. Since then, OWASP added 2 chars in that list: - Tab (0x09) - Carriage return (0x0D) This makes our previous prefix char (Tab `\t`) part of the vulnerable characters, and [OWASP suggests](https://owasp.org/www-community/attacks/CSV_Injection) using the single quote `'` for prefixing the value. Resolution ---------- Symfony now follows the OWASP recommendations and use the single quote `'` to prefix formulas and adds the prefix to cells starting by `\t`, `\r` as well as `=`, `+`, `-` and `@`. The patch for this issue is available [here](https://github.com/symfony/symfony/commit/3da6f2d45e7536ccb2a26f52fbaf340917e208a8) for branch 4.4. Credits ------- We would like to thank Jake Barwell for reporting the issue and Jérémy Derussé for fixing the issue.

CVE-2021-41270 Affected Symfony/serializer Versions

4 component(s)
Fixed Versions:
5.3.124.4.35
Product / Package Ecosystem Affected Versions Fixed Version
symfony/serializer
Packagist
≥ 5.0.0
< 5.3.12
5.3.12
symfony/serializer
Packagist
≥ 4.1.0
< 4.4.35
4.4.35
symfony/symfony
Packagist
≥ 4.1.0
< 4.4.35
4.4.35
symfony/symfony
Packagist
≥ 5.0.0
< 5.3.12
5.3.12

References

GitHub Advisory / Wiki ADVISORY
https://github.com/symfony/symfony/security/advisories/GHSA-2xhg-w2g5-w95x
NVD — CVE-2021-41270 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-41270
Symfony/serializer Source Repository REPOSITORY
https://github.com/symfony/symfony/pull/44243
Security Fix Commit FIX COMMIT
https://github.com/symfony/symfony/commit/3da6f2d45e7536ccb2a26f52fbaf340917e208a8
Symfony/serializer Source Repository REPOSITORY
https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/serializer/CVE-2021-41270.yaml
Symfony/serializer Source Repository REPOSITORY
https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2021-41270.yaml
Symfony/serializer Source Repository REPOSITORY
https://github.com/symfony/symfony
Symfony/serializer Release RELEASE
https://github.com/symfony/symfony/releases/tag/v5.3.12
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3BPT4SF6SIXFMZARDWED5T32J7JEH3EP
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QSREFD2TJT5LWKM6S4MD3W26NQQ5WJUP
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/3BPT4SF6SIXFMZARDWED5T32J7JEH3EP
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QSREFD2TJT5LWKM6S4MD3W26NQQ5WJUP
symfony.com/cve-2021-41270 WEB
https://symfony.com/cve-2021-41270

Frequently Asked Questions

What is CVE-2021-41270?
CVE-2021-41270 is a security vulnerability in Symfony/serializer involving CSV Injection in symfony/serializer under CWE-1236: Improper Neutralization of Formula Elements in a CSV File.
Which Symfony/serializer versions are affected?
Affected versions include releases prior to 5.3.12, 4.4.35 across affected packages: symfony/serializer, symfony/symfony.
What version fixes CVE-2021-41270?
Upgrading to 5.3.12, 4.4.35 (or the latest patched release for your respective branch) resolves the vulnerability.
Is symfony/serializer affected?
Yes, symfony/serializer is affected in releases prior to 5.3.12, 4.4.35. Upgrade your dependency to 5.3.12, 4.4.35 or later.
Is symfony/symfony affected?
Yes, symfony/symfony is affected in releases prior to 4.4.35, 5.3.12. Upgrade your dependency to 4.4.35, 5.3.12 or later.
What is the CVSS score of CVE-2021-41270?
CVE-2021-41270 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2021-41270?
CVE-2021-41270 is classified under CWE-1236: Improper Neutralization of Formula Elements in a CSV File (The product saves user-provided information into a Comma-Separated Value (CSV) file, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as a command when the file is opened by a spreadsheet product.).
How can I check Packagist dependencies for CVE-2021-41270?
Run the dependency tree command: 'inspect dependencies for symfony/serializer'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2xhg-w2g5-w95x",
  "modified" : "2024-02-05T11:14:05Z",
  "published" : "2021-11-24T21:01:23Z",
  "aliases" : [ "CVE-2021-41270" ],
  "summary" : "CSV Injection in symfony/serializer",
  "details" : "Description\n-----------\n\nCSV Injection, also known as Formula Injection, occurs when websites embed untrusted input inside CSV files. When a spreadsheet program opens a CSV, any cell starting with `=` is interpreted by the software as a formula and could be abused by an attacker.\n\nIn Symfony 4.1, we've added the opt-in `csv_escape_formulas` option in `CsvEncoder`, to prefix all cells starting by  `=`, `+`, `-` or `@` by a tab `\\t`. \n\nSince then, OWASP added 2 chars in that list: \n- Tab (0x09)\n- Carriage return (0x0D)\n\nThis makes our previous prefix char (Tab `\\t`) part of the vulnerable characters, and [OWASP suggests](https://owasp.org/www-community/attacks/CSV_Injection) using the single quote `'` for prefixing the value.\n\nResolution\n----------\n\nSymfony now follows the OWASP recommendations and use the single quote `'` to prefix formulas and adds the prefix to cells starting by `\\t`, `\\r` as well as `=`, `+`, `-` and `@`.\n\nThe patch for this issue is available [here](https://github.com/symfony/symfony/commit/3da6f2d45e7536ccb2a26f52fbaf340917e208a8) for branch 4.4.\n\nCredits\n-------\n\nWe would like to thank Jake Barwell for reporting the issue and Jérémy Derussé for fixing the issue.\n",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "symfony/serializer"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0"
      }, {
        "fixed" : "5.3.12"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "symfony/serializer"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.1.0"
      }, {
        "fixed" : "4.4.35"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "symfony/symfony"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.1.0"
      }, {
        "fixed" : "4.4.35"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "symfony/symfony"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0"
      }, {
        "fixed" : "5.3.12"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/symfony/symfony/security/advisories/GHSA-2xhg-w2g5-w95x"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-41270"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/symfony/symfony/pull/44243"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/symfony/symfony/commit/3da6f2d45e7536ccb2a26f52fbaf340917e208a8"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/serializer/CVE-2021-41270.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2021-41270.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/symfony/symfony"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/symfony/symfony/releases/tag/v5.3.12"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3BPT4SF6SIXFMZARDWED5T32J7JEH3EP"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QSREFD2TJT5LWKM6S4MD3W26NQQ5WJUP"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/3BPT4SF6SIXFMZARDWED5T32J7JEH3EP"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QSREFD2TJT5LWKM6S4MD3W26NQQ5WJUP"
  }, {
    "type" : "WEB",
    "url" : "https://symfony.com/cve-2021-41270"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1236" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-11-24T20:04:02Z",
    "nvd_published_at" : "2021-11-24T19:15:00Z"
  }
}