CVE-2021-21708

CRITICALNVD 8.29.8▲
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-02-28. NVD baseline CVSS 8.2; sources differ by 1.6.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 3%CVSS: 8.2Exploit: None knownExposed: 0

A fix is available — apply it.

In PHP versions 7.4.x below 7.4.28, 8.0.x below 8.0.16, and 8.1.x below 8.1.3, when using filter functions with FILTER_VALIDATE_FLOAT filter and min/max limits, if the filter fails, there is a possibility to trigger use of allocated memory after free, which can result it crashes, and potentially in overwrite of other memory chunks and RCE. This issue affects: code that uses FILTER_VALIDATE_FLOAT with min/max limits.

CVSS v3
8.2
EG Score
9.8(medium)
EG Risk
50(Track)
EG Risk 50/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation3% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
3%
EPSS %ILE
86%
KEV
Not listed

Published

February 27, 2022

Last Modified

November 21, 2024

Advisory Details (3)

Auto-updated Sep 8, 2026
No patch confirmed yet.
generic

NetApp Product Security

https://security.netapp.com/advisory/ntap-20220325-0004/
generic

PHP: Multiple Vulnerabilities (GLSA 202209-20) — Gentoo security

https://security.gentoo.org/glsa/202209-20
generic

PHP :: Sec Bug #81708 :: UAF due to php_filter_float() failing for ints

https://bugs.php.net/bug.php?id=81708

Vendor Advisories for CVE-2021-21708(5)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(6)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuphp8.0-imap (8.0.8-1ubuntu0.2) @ impish2026-05-26ubuntu
redhatphp:7.4-8040020250311105031.d7c090452025-03-20redhat
redhatphp:7.4-8060020250311104929.5caa48ff2025-03-18redhat
redhatphp-0:8.0.20-3.el92022-11-15redhat
redhatphp:8.0-8070020220801083134.afd00e682022-11-08redhat
redhatphp:7.4-8070020220707122009.afd00e682022-11-08redhat

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

(1 across 1 ecosystem)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
php7.47.4.21-1+deb11u1, 7.4.25-1+deb11u1, 7.4.26-17.4.28-1+deb11u1—

Weakness Classification(1)

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

Additional Vendor Advisories

(2)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 8× in last 7d / 29× 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.

Showing the most recent 100 of 146 total refreshes for this CVE.

  1. 2026-09-07 15:58 UTCEPSS rescore
  2. 2026-09-06 13:44 UTCEPSS rescore
  3. 2026-09-06 13:44 UTCEPSS rescore
  4. 2026-09-05 20:00 UTCOSV refresh
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  21. 2026-08-19 07:02 UTCOSV refresh
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  24. 2026-08-16 14:52 UTCEPSS rescore
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  1. 2026-08-15 01:27 UTCEPSS rescore
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  5. 2026-08-09 13:43 UTCEPSS rescore
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  8. 2026-08-06 13:43 UTCEPSS rescore
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  11. 2026-08-04 10:34 UTCEPSS rescore
  12. 2026-08-04 02:57 UTCOSV refresh
  13. 2026-08-03 10:32 UTCEPSS rescore
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  22. 2026-07-23 14:15 UTCEPSS rescore
  23. 2026-07-23 01:57 UTCEG score recompute
  24. 2026-07-22 22:43 UTCEG score recompute
  25. 2026-07-22 14:05 UTCEPSS rescore
  26. 2026-07-21 15:22 UTCEPSS rescore
  27. 2026-07-21 15:22 UTCEPSS rescore
  28. 2026-07-20 17:04 UTCEPSS rescore
  29. 2026-07-19 14:28 UTCEPSS rescore
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  31. 2026-07-18 10:02 UTCEPSS rescore
  32. 2026-07-17 21:59 UTCOSV refresh
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  42. 2026-07-09 19:07 UTCEPSS rescore
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  44. 2026-07-07 13:43 UTCEPSS rescore
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  50. 2026-07-04 06:29 UTCEPSS rescore
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  52. 2026-07-02 16:57 UTCEPSS rescore
  53. 2026-07-01 15:03 UTCEPSS rescore
  54. 2026-06-30 23:20 UTCEPSS rescore
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  56. 2026-06-29 19:32 UTCOSV refresh
  57. 2026-06-29 14:04 UTCEPSS rescore
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  72. 2026-06-21 01:58 UTCEPSS rescore
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  74. 2026-06-19 19:24 UTCEPSS rescore
  75. 2026-06-19 19:24 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-21708?
CVE-2021-21708 is a critical vulnerability published on February 27, 2022. In PHP versions 7.4.x below 7.4.28, 8.0.x below 8.0.16, and 8.1.x below 8.1.3, when using filter functions with FILTERVALIDATEFLOAT filter and min/max limits, if the filter fails, there is a possibility to trigger use of allocated memory after free, which can result it crashes, and potentially in…
When was CVE-2021-21708 disclosed?
CVE-2021-21708 was first published in the National Vulnerability Database on February 27, 2022, 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-2021-21708 actively exploited?
CVE-2021-21708 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 3% probability of exploitation in the next 30 days, which ranks it in the top 13.5% of all scored CVEs.
What is the CVSS score of CVE-2021-21708?
CVE-2021-21708 has a CVSS v3 base score of 8.2 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.8.
How do I remediate CVE-2021-21708?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-21708, 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.

Dependency Blast Radius

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