CVE-2026-33523

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

Score 6.5 from GitHub Security Advisory published 2026-05-04. NVD baseline CVSS 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.5Exploit: None knownExposed: 0

A fix is available — apply it.

HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised backend servers.

This issue affects Apache HTTP Server: from through 2.4.66.

Users are recommended to upgrade to version 2.4.67, which fixes the issue.

CVSS v3
6.5
EG Score
6.5(medium)
EG Risk
44(Track)
EG Risk 44/100SSVC: 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
Severity65% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
37%
KEV
Not listed

Published

May 4, 2026

Last Modified

May 4, 2026

Advisory Details (2)

Auto-updated May 4, 2026
⚠️ Active exploitation confirmed. Patch available.
generic

oss-security - CVE-2026-33523: Apache HTTP Server: multiple modules: HTTP response splitting forwarding malicious status line

http://www.openwall.com/lists/oss-security/2026/05/04/23
generic Patch Available🔴 Active Exploitation

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

https://httpd.apache.org/security/vulnerabilities_24.html

Vendor Advisories for CVE-2026-33523(2)

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

Patch Availability(3)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuapache2-utils (2.4.66-2ubuntu2.1) @ resolute2026-08-23ubuntu
ubuntuapache2-utils (2.4.18-2ubuntu3.17+esm19) @ xenial2026-08-23ubuntu
redhathttpd-main-2.4.67-1.hum12026-05-13redhat

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

(9 across 9 ecosystems)
Alpine:v3.20(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.67-r0—
Alpine:v3.21(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.67-r0—
Alpine:v3.22(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.67-r0—
Alpine:v3.23(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.67-r0—
Alpine:v3.24(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.67-r0—
Debian:11(1)
PackageVulnerable rangeFixed inDependents
apache22.4.48-3.1 ... 2.4.66-8 (82 versions)2.4.67-1~deb11u1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
apache22.4.57-2 ... 2.4.67-1~deb12u1 (46 versions)2.4.67-1~deb12u2—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
apache22.4.65-2 ... 2.4.67-1~deb13u1 (22 versions)2.4.67-1~deb13u2—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
apache22.4.65-2 ... 2.4.67-1~deb13u3 (24 versions)2.4.67-1—

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 / 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.

Showing the most recent 100 of 223 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-33523?
CVE-2026-33523 is a medium vulnerability published on May 4, 2026. HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised backend servers. This issue affects Apache HTTP Server: from through 2.4.66. Users are recommended to upgrade to version 2.4.67, which fixes the issue.
When was CVE-2026-33523 disclosed?
CVE-2026-33523 was first published in the National Vulnerability Database on May 4, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-33523 actively exploited?
CVE-2026-33523 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 62.7% of all scored CVEs.
What is the CVSS score of CVE-2026-33523?
CVE-2026-33523 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-33523?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-33523, 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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