# CVE-2021-21424: Prevent user enumeration using Guard or the new Authenticator-based Security > Attackers can enumerate valid usernames via inconsistent error responses in Symfony's user switching feature, exposing user existence information. - **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 13 May 2021 - **Updated:** 3 Aug 2024 - **Also known as:** BIT-symfony-2021-21424, DEBIAN-CVE-2021-21424, GHSA-5pv8-ppvj-4h68, UBUNTU-CVE-2021-21424 ## What is CVE-2021-21424? CVE-2021-21424 is a medium-severity vulnerability in Fedoraproject Fedora, published on 13 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description Symfony is a PHP framework for web and console applications and a set of reusable PHP components. The ability to enumerate users was possible without relevant permissions due to different handling depending on whether the user existed or not when attempting to use the switch users functionality. We now ensure that 403s are returned whether the user exists or not if a user cannot switch to a user or if the user does not exist. The patch for this issue is available for branch 3.4. Weakness: CWE-203 (Observable Discrepancy), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) ## Which versions are affected by CVE-2021-21424? 35 open source packages ship an affected version, including symfony/security, symfony and lexik/jwt-authentication-bundle. It affects 2 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `symfony/security` | Packagist | From 2.8.0 | 3.4.49 | | `symfony/security` | Packagist | From 2.8.0 | 3.4.49 | | `symfony/security` | Packagist | From 4.0.0 | 4.4.24 | | `symfony/security` | Packagist | From 4.0.0 | 4.4.24 | | `symfony/security` | Packagist | From 5.0.0 | 5.2.8 | | `symfony/security` | Packagist | From 5.0.0 | 5.2.8 | | `symfony` | Bitnami | From 2.8.0 | 3.4.48, 4.4.23, 5.2.8 | | `lexik/jwt-authentication-bundle` | Packagist | From 2.0.0 | 2.10.7 | | `lexik/jwt-authentication-bundle` | Packagist | From 2.0.0 | 2.10.7 | | `lexik/jwt-authentication-bundle` | Packagist | From 2.11.0 | 2.11.3 | | `lexik/jwt-authentication-bundle` | Packagist | From 2.11.0 | 2.11.3 | | `symfony/maker-bundle` | Packagist | From 1.27.0 | 1.29.2 | | `symfony/maker-bundle` | Packagist | From 1.27.0 | 1.29.2 | | `symfony/maker-bundle` | Packagist | From 1.30.0 | 1.31.1 | | `symfony/maker-bundle` | Packagist | From 1.30.0 | 1.31.1 | | `symfony/security-core` | Packagist | From 2.8.0 | 3.4.48 | | `symfony/security-core` | Packagist | From 2.8.0 | 3.4.48 | | `symfony/security-core` | Packagist | From 4.0.0 | 4.4.23 | | `symfony/security-core` | Packagist | From 4.0.0 | 4.4.23 | | `symfony/security-core` | Packagist | From 5.0.0 | 5.2.8 | | `symfony/security-core` | Packagist | From 5.0.0 | 5.2.8 | | `symfony/security-guard` | Packagist | From 2.8.0 | 3.4.48 | | `symfony/security-guard` | Packagist | From 2.8.0 | 3.4.48 | | `symfony/security-guard` | Packagist | From 4.0.0 | 4.4.23 | | `symfony/security-guard` | Packagist | From 4.0.0 | 4.4.23 | | `symfony/security-guard` | Packagist | From 5.0.0 | 5.2.8 | | `symfony/security-guard` | Packagist | From 5.0.0 | 5.2.8 | | `symfony/security-http` | Packagist | From 5.1.0 | 5.2.8 | | `symfony/security-http` | Packagist | From 5.1.0 | 5.2.8 | | `symfony/symfony` | Packagist | From 2.8.0 | 3.4.49 | | `symfony/symfony` | Packagist | From 2.8.0 | 3.4.49 | | `symfony/symfony` | Packagist | From 4.0.0 | 4.4.24 | | `symfony/symfony` | Packagist | From 4.0.0 | 4.4.24 | | `symfony/symfony` | Packagist | From 5.0.0 | 5.2.9 | | `symfony/symfony` | Packagist | From 5.0.0 | 5.2.9 | Products: Fedoraproject Fedora, Sensiolabs Symfony. ## How do I fix CVE-2021-21424? Upgrade symfony/security to a fixed version for your release line: 3.4.49, 4.4.24 or 5.2.8. ## Is CVE-2021-21424 being exploited? There is no known exploitation of CVE-2021-21424 in the wild and no public exploit code. Public exploit code: - El WebProfiler de Symfony expone rutas internas del servidor si no está deshabilitado en producción (github_poc): https://github.com/moften/CVE-2021-21424 - CVE-2021-21424 - CRLF Injection - CVE-2021-41268 - Host Header Injection - CVE-2022-24894 - WebProfiler abierto - CVE-2019-10909 - Directory Traversal (github_poc): https://github.com/moften/Symfony-CVE-Scanner-PoC- ## Other vulnerabilities in Fedoraproject Fedora - [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild) - [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild) - [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild) - [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild) - [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-21424 and fix it if it is affected. What it is: CVE-2021-21424 is a medium-severity vulnerability in Fedoraproject Fedora, published on 13 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-21424 in the wild and no public exploit code. Affected packages and fixed versions: - symfony/security (Packagist): affected from 2.8.0; fixed in 3.4.49 - symfony/security (Packagist): affected from 2.8.0; fixed in 3.4.49 - symfony/security (Packagist): affected from 4.0.0; fixed in 4.4.24 - symfony/security (Packagist): affected from 4.0.0; fixed in 4.4.24 - symfony/security (Packagist): affected from 5.0.0; fixed in 5.2.8 - symfony/security (Packagist): affected from 5.0.0; fixed in 5.2.8 - symfony (Bitnami): affected from 2.8.0; fixed in 3.4.48, 4.4.23, 5.2.8 - lexik/jwt-authentication-bundle (Packagist): affected from 2.0.0; fixed in 2.10.7 - lexik/jwt-authentication-bundle (Packagist): affected from 2.0.0; fixed in 2.10.7 - lexik/jwt-authentication-bundle (Packagist): affected from 2.11.0; fixed in 2.11.3 - lexik/jwt-authentication-bundle (Packagist): affected from 2.11.0; fixed in 2.11.3 - symfony/maker-bundle (Packagist): affected from 1.27.0; fixed in 1.29.2 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-21424/ (Markdown: https://insights.sbomify.com/CVE-2021-21424/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21424 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21424 - OSV: https://osv.dev/vulnerability/CVE-2021-21424 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-21424/ Summaries are generated and may contain mistakes; the official description above is the record.