CVE-2021-21424

mediumpriority · track · 32EPSS 0.016 · 76 %ileexploit · PoCEURUUS
grimoire priorityP1 · Urgent
Exploitable?
Public exploit
2 exploits · PoC
Likely / severe?
1.64% (76th) EPSS
CVSS 5 · medium
Is it mine?
37 products
Check your exposure
Who says so?
5 sources
cnnvd · enisa_euvd · fstec_bdu · osv

EPSS · scored 2026-10-27

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.

01

cvss

Technical severity, 0–10. One row per scoring source.

5.3
010

base score 0–10 · higher = more severe · hover a vector to decode

v2.05mediumAV:N/AC:L/Au:N/C:P/I:N/A:Nprimary · NVD / NIST USexploitability 10 · impact 2.9
v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:Nprimary · NVD / NIST USexploitability 3.9 · impact 1.4
v3.15.3mediumAV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:Nsecondary · FSTEC (BDU) RU
v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:Nsecondary · ENISA EU
v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:Nsecondary · security-advisories@github.comexploitability 3.9 · impact 1.4
v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:Nsecondary · OSV
v3.15mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:Psecondary · CVSS-BT (t0sche)
02

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-203USprimaryCWE-200USCWE-200USCWE-200USCWE-203US
03

exploits (2)

Public proof-of-concept and weaponised exploit code.

04

affected products (37)

Products and version ranges known to be affected.

showing 20 of 37
05

advisories (2)

Vendor and ecosystem advisories describing this.

  • GHSA-5pv8-ppvj-4h68Prevent user enumeration using Guard or the new Authenticator-based Security2021-05-13ghsa · osvUS

    Description ----------- The ability to enumerate users was possible without relevant permissions due to different exception messages depending on whether the user existed or not. It was also possible to enumerate users by using a timing attack, by comparing time elapsed when authenticating an existing user and authenticating a non-existing user. Resolution ---------- We now ensure that 403s are returned whether the user exists or not if the password is invalid or if the user does not exist. The patch for this issue is available [here](https://github.com/symfony/symfony/commit/2a581d22cc621b33d5464ed65c4bc2057f72f011) for branch 3.4. Credits ------- I would like to thank James Isaac and Mathias Brodala for reporting the issue and Robin Chalas for fixing the issue.

  • BIT-symfony-2021-214242024-03-06vendor · osvUS

    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.

06

also known as (6)

Other names and identifiers for this entity.

07

sources

Which sources assert this record, and when.

cnnvdenisa_euvdfstec_bduosvnvdNVDCVE.orgMITRE
published 2021-05-13modified 2026-06-17
09

references (25)

External citations — patches, advisories, analysis.

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