HOMEVULNERABILITIESCVE-2021-21424
MEDIUM

CVE-2021-21424

CWE-200Published: May 13, 2021· Updated: Jun 17, 2026

5.3
CVSS v3.1

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.

NVD Source

Technical Analysis

CVE-2021-21424 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

From a weakness classification perspective (CWE-200): Information exposure vulnerabilities leak sensitive data to unauthorized actors.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityLow
IntegrityNone
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected Vendors & Products

Fedora1 product(s)
fedora
sensiolabs1 product(s)
symfony
Source: NVD CPE · 3 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://github.com/symfony/symfony/commit/2a581d22cc621b33d5464ed65c4bc2057f72f011
PATCHhttps://github.com/symfony/symfony/security/advisories/GHSA-5pv8-ppvj-4h68
PATCHhttps://github.com/symfony/symfony/commit/2a581d22cc621b33d5464ed65c4bc2057f72f011
PATCHhttps://github.com/symfony/symfony/security/advisories/GHSA-5pv8-ppvj-4h68

All References (14)

→
https://github.com/symfony/symfony/commit/2a581d22cc621b33d5464ed65c4bc2057f72f011Patch · Third Party Advisory
→
https://github.com/symfony/symfony/security/advisories/GHSA-5pv8-ppvj-4h68Patch · Third Party Advisory
→
https://lists.debian.org/debian-lts-announce/2023/07/msg00014.html
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KENRNLB3FYXYGDWRBH2PDBOZZKOD7VY4/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RH7TMM5CHQYBFFGXWRPJDPB3SKCZXI2M/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UC7BND775DVZDQT3RMGD2HVB2PKLJDJW/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VRUS2H2SSOQWNLBD35SKIWIDQEMV2PD3/
→
https://github.com/symfony/symfony/commit/2a581d22cc621b33d5464ed65c4bc2057f72f011Patch · Third Party Advisory
→
https://github.com/symfony/symfony/security/advisories/GHSA-5pv8-ppvj-4h68Patch · Third Party Advisory
→
https://lists.debian.org/debian-lts-announce/2023/07/msg00014.html
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KENRNLB3FYXYGDWRBH2PDBOZZKOD7VY4/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RH7TMM5CHQYBFFGXWRPJDPB3SKCZXI2M/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UC7BND775DVZDQT3RMGD2HVB2PKLJDJW/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VRUS2H2SSOQWNLBD35SKIWIDQEMV2PD3/

Quick Facts

CVE IDCVE-2021-21424
CVSS Score5.3 / 10
SeverityMEDIUM
WeaknessCWE-200
CISA KEVNo
Affected2 vendor(s)
PublishedMay 13, 2021

Related CVEs (CWE-200)

CVE-2025-29270
10.0
CVE-2020-13702
10.0
CVE-2026-27604
10.0
CVE-2014-9162
10.0
CVE-2025-61481
10.0
CVE-2008-3010
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-21424 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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