CVE-2021-3603

HIGHNVD 8.18.1—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.1 under NVD CVSS v3. EPSS exploit probability: 2.3%, top 19% 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
Trending — 3 sources updated this week
8.1
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 8.1Exploit: NoneExposed: 0

A fix is available — apply it.

PHPMailer 6.4.1 and earlier contain a vulnerability that can result in untrusted code being called (if such code is injected into the host project's scope by other means). If the $patternselect parameter to validateAddress() is set to 'php' (the default, defined by PHPMailer::$validator), and the global namespace contains a function called php, it will be called in preference to the built-in validator of the same name. Mitigated in PHPMailer 6.5.0 by denying the use of simple strings as validator function names.

CVSS v3
8.1
EG Score
8.1(medium)
EG Risk
42(Track)
EG Risk 42/100SSVC: 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
Severity81% × 45%
Exploitation2% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
81.1%
KEV
Not listed

Published

June 17, 2021

Last Modified

November 21, 2024

References (8)

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulibphp-phpmailer (5.2.14+dfsg-2.3+deb9u2ubuntu0.1~esm1) @ bionic2026-05-26ubuntu

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

(1 across 1 ecosystem)
Packagist(1)
PackageVulnerable rangeFixed inDependents
phpmailer/phpmailerv5.2.10 ... v6.4.1 (52 versions)6.5.0—

Weakness Classification(1)

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 13× in last 7d / 50× 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 105 total refreshes for this CVE.

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

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-3603?
CVE-2021-3603 is a high vulnerability published on June 17, 2021. PHPMailer 6.4.1 and earlier contain a vulnerability that can result in untrusted code being called (if such code is injected into the host project's scope by other means). If the $patternselect parameter to validateAddress() is set to 'php' (the default, defined by PHPMailer::$validator), and the…
When was CVE-2021-3603 disclosed?
CVE-2021-3603 was first published in the National Vulnerability Database on June 17, 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-2021-3603 actively exploited?
CVE-2021-3603 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 81.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-3603?
CVE-2021-3603 has a CVSS v3 base score of 8.1 (NVD).
How do I remediate CVE-2021-3603?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-3603, 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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