CVE-2025-66376

CRITICALNVD 6.19.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2026-03-18), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 6.1 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 4 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 22%CVSS: 6.1Exploit: cisa kev · ssvc active · epss top5pctExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

CVSS v3
6.1
EG Score
9.0(high)
EG Risk
81(Attend)
EG Risk 81/100SSVC: Attend

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
Severity90% × 45%
Exploitation100% × 40%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
22%
EPSS %ILE
97%
KEV
⚠ Exploited

Published

January 5, 2026

Last Modified

June 17, 2026

Advisory Details (6)

Auto-updated Jun 11, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: cisa.
cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376
generic

Zimbra Security Advisories - Zimbra :: Tech Center

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
generic

Zimbra Responsible Disclosure Policy - Zimbra :: Tech Center

https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy
generic

Zimbra Releases/10.1.13 - Zimbra :: Tech Center

https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes
generic

Zimbra Releases/10.0.18 - Zimbra :: Tech Center

https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes
generic🔴 Active Exploitation

Security Center - Zimbra :: Tech Center

https://wiki.zimbra.com/wiki/Security_Center

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 55× in last 7d / 225× 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 486 total refreshes for this CVE.

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

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Frequently asked(6)

What is CVE-2025-66376?
CVE-2025-66376 is a critical vulnerability published on January 5, 2026. Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.
When was CVE-2025-66376 disclosed?
CVE-2025-66376 was first published in the National Vulnerability Database on January 5, 2026, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2025-66376 actively exploited?
Yes. CISA added CVE-2025-66376 to the Known Exploited Vulnerabilities catalog on March 18, 2026, affecting Synacor Zimbra Collaboration Suite (ZCS). KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2025-66376?
CVE-2025-66376 has a CVSS v3 base score of 6.1 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2025-66376?
CVE-2025-66376 affects Synacor Zimbra Collaboration Suite (ZCS). The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.
How do I remediate CVE-2025-66376?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2025-66376, 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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