CVE-2021-40438

CRITICALNVD 9.09.0—
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2021-12-01), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 9.0 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 3 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • 1,199 internet-exposed hosts are running an affected version right now
  • Actively exploited in the wild (CISA-KEV)
  • Linked to ransomware campaigns
CISA-KEV: ExploitedEPSS PROB: 100%CVSS: 9.0Exploit: cisa kev · ssvc active · kev ransomware · epss top5pct · epss high · public exploitExposed: 1,199

A fix is available — apply it.

A crafted request uri-path can cause mod_proxy to forward the request to an origin server choosen by the remote user. This issue affects Apache HTTP Server 2.4.48 and earlier.

Live · internet exposure

1,199 internet-exposed hosts are running an affected version of CVE-2021-40438 right now.

across 75 countries (United States, Japan, Germany, France, Poland)top: http_server🔒 ransomware-linked
See the live KEV-Exposure radar →Found passively from public internet-scan data — aggregate, host-redacted.

EchelonGraph is the only CVE feed that fuses live vulnerability intelligence with its own live internet-exposure radar — so you see not just that a CVE is exploited, but how much of the internet is exposed to it right now.

CVSS v3
9.0
EG Score
9.0(high)
EG Risk
96(Act)
EG Risk 96/100SSVC: Act

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%
Automatability100% × 15%
Action: Fix now — active exploitation, automatable, high impact.
EPSS PROB
100%
EPSS %ILE
100%
KEV
⚠ Exploited

Published

September 16, 2021

Last Modified

August 6, 2026

Advisory Details (9)

Auto-updated Jun 2, 2026
⚠️ Active exploitation confirmed. Patch available.
generic Patch Available

[SECURITY] [DLA 2776-1] apache2 security update

https://lists.debian.org/debian-lts-announce/2021/10/msg00001.html
generic
https://lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3E
generic
https://lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E
generic
https://lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E
generic
https://lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E
generic
https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E
generic
https://lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E
generic
https://lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E
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-2021-40438(7)

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

Patch Availability(9)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuapache2-bin (2.4.46-4ubuntu1.2) @ hirsute2026-09-08ubuntu
ubuntulibapache2-mod-proxy-html (1:2.4.7-1ubuntu4.22+esm2) @ trusty2026-09-08ubuntu
redhathttpd-0:2.4.6-90.el7_7.12021-10-14redhat
redhathttpd:2.4-8010020211008125020.c27ad7f82021-10-13redhat
redhathttpd:2.4-8020020211008164029.4cda2c842021-10-13redhat
redhathttpd:2.4-8040020211008164252.522a0ee42021-10-12redhat
redhathttpd24-httpd-0:2.4.34-22.el7.12021-10-11redhat
redhatpatch2021-10-07redhat
redhatjbcs-httpd24-mod_security-0:2.9.2-65.GA.jbcs.el72021-10-07redhat

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

(20 across 20 ecosystems)
Alpine:v3.11(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.12(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.13(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.14(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.15(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.16(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.17(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.18(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.19(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.20(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.21(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.22(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.23(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Alpine:v3.24(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-r0—
Debian:10(1)
PackageVulnerable rangeFixed inDependents
apache22.4.38-3 ... 2.4.38-3+deb10u5 (6 versions)2.4.38-3+deb10u6—
Debian:11(1)
PackageVulnerable rangeFixed inDependents
apache22.4.48-3.1 ... 2.4.51-1~bpo10+2 (15 versions)2.4.51-1~deb11u1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
apache2—2.4.49-1—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
apache22.4.25-3 ... 2.4.25-3+deb9u9 (11 versions)2.4.25-3+deb9u11—

Weakness Classification(1)

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

Additional Vendor Advisories

(3)

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 84× in last 7d / 364× 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 1,201 total refreshes for this CVE.

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

Publicly available exploits

(6 references)

Working exploit code is in the public domain (5 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCsergiovks/CVE-2021-40438-Apache-2.4.48-SSRF-exploit
    First seen Dec 12, 2023

    CVE-2021-40438 Apache <= 2.4.48 SSRF exploit

    Open source ↗
  • GitHub PoCKashkovsky/CVE-2021-40438
    First seen Apr 3, 2022

    Apache forward request CVE

    Open source ↗
  • GitHub PoCBabyTeam1024/CVE-2021-40438
    First seen Oct 28, 2021
    Open source ↗
  • GitHub PoCsixpacksecurity/CVE-2021-40438
    First seen Oct 24, 2021

    CVE-2021-40438 exploit PoC with Docker setup.

    Open source ↗
  • GitHub PoCxiaojiangxl/CVE-2021-40438
    First seen Oct 18, 2021
    Open source ↗
  • Nucleihttp/cves/2021/CVE-2021-40438.yaml
    First seen Jan 1, 2021

    Apache <= 2.4.48 Mod_Proxy - Server-Side Request Forgery

    Open source ↗

Frequently asked(6)

What is CVE-2021-40438?
CVE-2021-40438 is a critical vulnerability published on September 16, 2021. A crafted request uri-path can cause mod_proxy to forward the request to an origin server choosen by the remote user. This issue affects Apache HTTP Server 2.4.48 and earlier.
When was CVE-2021-40438 disclosed?
CVE-2021-40438 was first published in the National Vulnerability Database on September 16, 2021, with the most recent update on August 6, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-40438 actively exploited?
Yes. CISA added CVE-2021-40438 to the Known Exploited Vulnerabilities catalog on December 1, 2021, affecting Apache Apache. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2021-40438?
CVE-2021-40438 has a CVSS v3 base score of 9.0 (NVD).
Which products are affected by CVE-2021-40438?
CVE-2021-40438 affects Apache Apache. 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-2021-40438?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-40438, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-40438

Explore →

Is Your Infrastructure Affected by CVE-2021-40438?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs