CVE-2026-39963

MEDIUMNVD 6.96.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.9 under NVD CVSS v3. EPSS exploit probability: 0.1%, top 77% 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
Elevated
6.9
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 6.9Exploit: NoneExposed: 0

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

Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.

CVSS v3
6.9
EG Score
6.9(medium)
EPSS
13.2%
KEV
Not listed

Published

April 15, 2026

Last Modified

April 23, 2026

Advisory Details (2)

Auto-updated Jun 14, 2026
🔬 Proof of concept available. Patch available. Sources: github_release, github.
github Patch Available🟡 PoC Available

Host Header Injection allows authentication cookie scoping to attacker-controlled domain in functions_config.inc.php · Advisory · s9y/Serendipity · GitHub

https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf
github_release Patch Available

Serendipity 2.6.0

Patch available: s9y/Serendipity 2.6.0

https://github.com/s9y/Serendipity/releases/tag/2.6.0

Affected Packages

(1 across 1 ecosystem)
Packagist(1)
PackageVulnerable rangeFixed inDependents
s9y/serendipity2.0.0 ... 2.6-beta1 (31 versions)2.6.0—

Weakness Classification(1)

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

Data Freshness Timeline

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

Frequently asked(5)

What is CVE-2026-39963?
CVE-2026-39963 is a medium vulnerability published on April 15, 2026. Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the serendipitysetCookie() function in include/functionsconfig.inc.php uses $SERVER['HTTPHOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such…
When was CVE-2026-39963 disclosed?
CVE-2026-39963 was first published in the National Vulnerability Database on April 15, 2026, with the most recent update on April 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-39963 actively exploited?
CVE-2026-39963 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 13.2% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-39963?
CVE-2026-39963 has a CVSS v3 base score of 6.9 (NVD).
How do I remediate CVE-2026-39963?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-39963, 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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