CVE-2021-21424

MEDIUMNVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.3 under NVD CVSS v3. EPSS exploit probability: 0.3%, top 43% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
5.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 2%CVSS: 5.3Exploit: NoneExposed: 0

A fix is available — apply it.

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.

CVSS v3
5.3
EG Score
5.3(medium)
EPSS
74.9%
KEV
Not listed

Published

May 13, 2021

Last Modified

November 21, 2024

References (14)

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuphp-symfony-console (4.3.8+dfsg-1ubuntu1+esm1) @ focal2026-05-26ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(7 across 1 ecosystem)
Packagist(7)
PackageVulnerable rangeFixed inDependents
lexik/jwt-authentication-bundlev2.11.0, v2.11.1, v2.11.22.11.3—
symfony/maker-bundlev1.30.0, v1.30.1, v1.30.2, v1.31.01.31.1—
symfony/securityv4.0.0 ... v4.4.9 (90 versions)4.4.24—
symfony/security-corev5.0.0 ... v5.2.7 (40 versions)5.2.8—
symfony/security-guardv5.0.0 ... v5.2.4 (37 versions)5.2.8—
symfony/security-httpv5.1.0 ... v5.2.7 (25 versions)5.2.8—
symfony/symfonyv5.0.0 ... v5.2.8 (41 versions)5.2.9—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 11× in last 7d / 48× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-21 15:22 UTCEPSS rescore
  2. 2026-07-21 15:22 UTCEPSS rescore
  3. 2026-07-20 17:04 UTCEPSS rescore
  4. 2026-07-19 14:28 UTCEPSS rescore
  5. 2026-07-19 02:26 UTCEPSS rescore
  6. 2026-07-18 20:59 UTCOSV refresh
  7. 2026-07-18 10:02 UTCEPSS rescore
  8. 2026-07-16 17:00 UTCEPSS rescore
  9. 2026-07-15 16:55 UTCEPSS rescore
  10. 2026-07-15 16:55 UTCEPSS rescore
  11. 2026-07-15 01:57 UTCEPSS rescore
  12. 2026-07-13 22:27 UTCEPSS rescore
  13. 2026-07-13 22:27 UTCEPSS rescore
  14. 2026-07-13 06:10 UTCEPSS rescore
  15. 2026-07-13 06:10 UTCEPSS rescore
  16. 2026-07-12 05:44 UTCEPSS rescore
  17. 2026-07-12 05:44 UTCEPSS rescore
  18. 2026-07-11 08:25 UTCEPSS rescore
  19. 2026-07-09 19:07 UTCEPSS rescore
  20. 2026-07-08 15:12 UTCEPSS rescore
  21. 2026-07-07 13:43 UTCEPSS rescore
  22. 2026-07-06 16:25 UTCEPSS rescore
  23. 2026-07-06 02:21 UTCEPSS rescore
  24. 2026-07-06 02:21 UTCEPSS rescore
  25. 2026-07-05 02:28 UTCEPSS rescore
Show 75 more
  1. 2026-07-05 02:28 UTCEPSS rescore
  2. 2026-07-04 06:29 UTCEPSS rescore
  3. 2026-07-04 06:29 UTCEPSS rescore
  4. 2026-07-02 16:57 UTCEPSS rescore
  5. 2026-07-01 15:03 UTCEPSS rescore
  6. 2026-07-01 03:48 UTCOSV refresh
  7. 2026-06-30 23:20 UTCEPSS rescore
  8. 2026-06-30 23:20 UTCEPSS rescore
  9. 2026-06-29 14:04 UTCEPSS rescore
  10. 2026-06-29 14:04 UTCEPSS rescore
  11. 2026-06-28 14:05 UTCEPSS rescore
  12. 2026-06-28 04:54 UTCEPSS rescore
  13. 2026-06-28 04:54 UTCEPSS rescore
  14. 2026-06-27 03:06 UTCEPSS rescore
  15. 2026-06-27 03:06 UTCEPSS rescore
  16. 2026-06-25 13:48 UTCEPSS rescore
  17. 2026-06-25 13:48 UTCEPSS rescore
  18. 2026-06-24 14:03 UTCEPSS rescore
  19. 2026-06-24 14:03 UTCEPSS rescore
  20. 2026-06-23 21:31 UTCEPSS rescore
  21. 2026-06-23 21:31 UTCEPSS rescore
  22. 2026-06-22 14:24 UTCEPSS rescore
  23. 2026-06-22 14:23 UTCEPSS rescore
  24. 2026-06-21 14:54 UTCEPSS rescore
  25. 2026-06-21 14:54 UTCEPSS rescore
  26. 2026-06-21 01:58 UTCEPSS rescore
  27. 2026-06-21 01:57 UTCEPSS rescore
  28. 2026-06-19 19:24 UTCEPSS rescore
  29. 2026-06-19 19:24 UTCEPSS rescore
  30. 2026-06-18 17:51 UTCEPSS rescore
  31. 2026-06-18 17:51 UTCEPSS rescore
  32. 2026-06-17 17:51 UTCEPSS rescore
  33. 2026-06-16 17:50 UTCEPSS rescore
  34. 2026-06-15 17:46 UTCEPSS rescore
  35. 2026-06-14 23:15 UTCEPSS rescore
  36. 2026-06-13 22:58 UTCEPSS rescore
  37. 2026-06-13 06:13 UTCOSV refresh
  38. 2026-06-12 23:10 UTCEPSS rescore
  39. 2026-06-12 23:10 UTCEPSS rescore
  40. 2026-06-11 13:58 UTCEPSS rescore
  41. 2026-06-10 22:16 UTCEPSS rescore
  42. 2026-06-10 22:16 UTCEPSS rescore
  43. 2026-06-10 13:20 UTCEPSS rescore
  44. 2026-06-08 14:15 UTCEPSS rescore
  45. 2026-06-08 14:15 UTCEPSS rescore
  46. 2026-06-07 15:23 UTCEPSS rescore
  47. 2026-06-07 15:23 UTCEPSS rescore
  48. 2026-06-06 13:46 UTCEPSS rescore
  49. 2026-06-06 13:46 UTCEPSS rescore
  50. 2026-06-06 13:46 UTCEPSS rescore
  51. 2026-06-05 22:45 UTCEPSS rescore
  52. 2026-06-05 22:45 UTCEPSS rescore
  53. 2026-06-05 06:09 UTCEPSS rescore
  54. 2026-06-05 06:09 UTCEPSS rescore
  55. 2026-06-05 06:08 UTCEPSS rescore
  56. 2026-06-04 13:10 UTCEPSS rescore
  57. 2026-06-02 20:11 UTCEPSS rescore
  58. 2026-06-02 20:11 UTCEPSS rescore
  59. 2026-06-01 13:50 UTCEPSS rescore
  60. 2026-06-01 13:50 UTCEPSS rescore
  61. 2026-05-31 22:29 UTCEPSS rescore
  62. 2026-05-31 22:29 UTCEPSS rescore
  63. 2026-05-31 00:15 UTCEPSS rescore
  64. 2026-05-31 00:15 UTCEPSS rescore
  65. 2026-05-29 13:42 UTCEPSS rescore
  66. 2026-05-28 13:43 UTCEPSS rescore
  67. 2026-05-28 13:43 UTCEPSS rescore
  68. 2026-05-27 13:39 UTCEPSS rescore
  69. 2026-05-26 16:39 UTCEG score recompute
  70. 2026-05-26 16:39 UTCVendor advisory
  71. 2026-05-26 13:42 UTCEPSS rescore
  72. 2026-05-26 13:42 UTCEPSS rescore
  73. 2026-05-26 07:17 UTCEPSS rescore
  74. 2026-05-26 07:17 UTCEPSS rescore
  75. 2026-05-24 16:49 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-21424?
CVE-2021-21424 is a medium vulnerability published on May 13, 2021. 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…
When was CVE-2021-21424 disclosed?
CVE-2021-21424 was first published in the National Vulnerability Database on May 13, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-21424 actively exploited?
CVE-2021-21424 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 74.9% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-21424?
CVE-2021-21424 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2021-21424?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-21424, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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