CVE-2021-44224

CRITICALNVD 8.29.0
EchelonGraph scoreHIGH confidence

“▲” beside the score: it is higher than NVD's CVSS score.

Score elevated to 9.0 because EPSS predicted 82% probability of exploitation within the next 30 days (99th percentile of EPSS-scored CVEs) when EchelonGraph scored this CVE. NVD baseline CVSS 8.2 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction (continuous uplift above 30%)
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
Trending — 5 sources updated this weekElevated
9.0EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • 2,049 internet-facing services (distinct ip:port) on record running an affected version — derived from Shodan data (© Shodan); a patched service can stay counted while its port stays open
  • High exploitation likelihood — EPSS 82%
CISA-KEV: Not listedEPSS PROB: 82%CVSS: 8.2Exploit: No code on recordExposed services: 2,049

A fix is available — apply it.

A crafted URI sent to httpd configured as a forward proxy (ProxyRequests on) can cause a crash (NULL pointer dereference) or, for configurations mixing forward and reverse proxy declarations, can allow for requests to be directed to a declared Unix Domain Socket endpoint (Server Side Request Forgery). This issue affects Apache HTTP Server 2.4.7 up to 2.4.51 (included).

Internet exposure · derived from Shodan data

2,049 internet-facing services (distinct ip:port) on record running a version that maps to CVE-2021-44224, in our KEV-Exposure radar’s Shodan-derived sample.

across 87 countries (United States, Germany, Japan, France, Netherlands)top: http_server
See the KEV-Exposure radar →Derived from Shodan data. Shodan data is owned by Shodan, which holds its copyright (© Shodan). EchelonGraph claims no ownership of it or copyright in it. Aggregate, host-redacted.

How it counts: every 12 hours, when Shodan query credits allow, the radar runs one Shodan query per tracked product, reads up to 100 ip:port services per query, and keeps a service when its banner version matches a CISA-KEV or high-EPSS CVE; a service is dropped when neither a search nor a Shodan InternetDB port re-check has refreshed it for 21 days. A re-check that finds the port still listed by Shodan InternetDB refreshes the service without re-reading the banner, so a patched service can stay counted while its port stays open. A count is a banner-version inference over a sample, not an exploit test and not an internet-wide census, and the unit is a service, not a machine: a machine answering on two ports counts twice.

CVSS v3
8.2
EG Score
9.0CRITICALhigh confidence
EG Risk
70
EG Risk 70/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity82% × 45%
Impact severity (EG Severity): CVSS 8.2 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation82% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's BOD 26-04 default: no one has published Automatable for this CVE, and CISA treats it as “no” for a CVE not in KEV.
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
82%
EPSS %ILE
99th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (9.0): severity, escalated by confirmed exploitation. This CVE's 9.0 is EPSS's lift toward 9.0 from its impact severity (EG Severity, CVSS 8.2 HIGH): a likelihood of exploitation, not impact.

EG Severity
8.2 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
82% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-22). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

December 20, 2021

Last Modified

November 21, 2024

Advisory Details (10)

Auto-updated Sep 9, 2026
Patch available.
Web page

Apache HTTPD: Multiple Vulnerabilities (GLSA 202208-20) — Gentoo security

https://security.gentoo.org/glsa/202208-20
Web page

[SECURITY] Fedora 34 Update: httpd-2.4.53-1.fc34 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Z7H26WJ6TPKNWV3QKY4BHKUKQVUTZJTD/
Web page

[SECURITY] Fedora 36 Update: httpd-2.4.53-1.fc36 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/X73C35MMMZGBVPQQCH7LQZUMYZNQA5FO/
Web page

[SECURITY] Fedora 35 Update: httpd-2.4.53-1.fc35 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RGWILBORT67SHMSLYSQZG2NMXGCMPUZO/
Web page

[SECURITY] Fedora 35 Update: httpd-2.4.52-1.fc35 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BFSWOH4X77CV7AH7C4RMHUBDWKQDL4YH/
Web page

oss-security - CVE-2021-44224: Apache HTTP Server: Possible NULL dereference or SSRF in forward proxy configurations in Apache HTTP Server 2.4.51 and earlier

http://www.openwall.com/lists/oss-security/2021/12/20/3
Web page

Full Disclosure: APPLE-SA-2022-05-16-2 macOS Monterey 12.4

http://seclists.org/fulldisclosure/2022/May/38
Web page

Full Disclosure: APPLE-SA-2022-05-16-3 macOS Big Sur 11.6.6

http://seclists.org/fulldisclosure/2022/May/35
Web page

Full Disclosure: APPLE-SA-2022-05-16-4 Security Update 2022-004 Catalina

http://seclists.org/fulldisclosure/2022/May/33
Web pageMentions a patch (unverified)

Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project

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

Patch Availability(6)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntuapache2-bin (2.4.48-3.1ubuntu3.2) @ impish2026-10-22ubuntu
ubuntuapache2-utils (2.4.18-2ubuntu3.17+esm4) @ xenial2026-10-22ubuntu
redhatjbcs-httpd24-httpd2022-10-26redhat
redhatjbcs-httpd24-httpd-0:2.4.51-28.el7jbcs2022-10-26redhat
redhathttpd24-httpd-0:2.4.34-23.el7.52022-09-29redhat
redhathttpd:2.4-8060020220321163517.d63f516d2022-05-10redhat

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

(19 across 19 ecosystems)
Alpine:v3.12(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.13(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.14(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.15(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.16(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.17(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.18(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.19(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.20(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.21(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.22(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.23(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Alpine:v3.24(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-r0: fixed in 2.4.52-r0
—
Debian:10(1)
PackageVulnerable rangeFix by version rangeDependents
apache22.4.38-3 ... 2.4.38-3+deb10u6 (7 versions)
  • every version up to 2.4.38-3+deb10u7: fixed in 2.4.38-3+deb10u7
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
apache22.4.48-3.1 ... 2.4.52-1~deb11u1 (20 versions)
  • every version up to 2.4.52-1~deb11u2: fixed in 2.4.52-1~deb11u2
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-1: fixed in 2.4.52-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-1: fixed in 2.4.52-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
apache2—
  • every version up to 2.4.52-1: fixed in 2.4.52-1
—
Debian:9(1)
PackageVulnerable rangeFix by version rangeDependents
apache22.4.25-3 ... 2.4.25-3+deb9u9 (12 versions)
  • every version up to 2.4.25-3+deb9u12: fixed in 2.4.25-3+deb9u12
—

Weakness Classification(1)

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

Additional Vendor Advisories

(4)

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 14× in last 7d / 27× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 80 of 111 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 20 repeat rows among the latest 100 are merged into the row they repeat. The 31 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-23 05:33 UTCEG score recompute
  2. 2026-10-23 05:33 UTCVendor advisory
  3. 2026-10-23 05:33 UTCGHSA enrichmentGHSA-92ww-hwmg-qq7p · GitHub severity HIGH · GitHub CVSS 8.2
  4. 2026-10-22 16:29 UTCEPSS rescoreEPSS 82% · 99th percentile
  5. 2026-10-22 07:09 UTCEG score recompute
  6. 2026-10-22 07:09 UTCVendor advisory
  7. 2026-10-22 07:09 UTCGHSA enrichmentGHSA-92ww-hwmg-qq7p · GitHub severity HIGH · GitHub CVSS 8.2
  8. 2026-10-21 16:28 UTCEPSS rescoreEPSS 82% · 99th percentile
  9. 2026-10-21 08:47 UTCEG score recompute
  10. 2026-10-21 08:47 UTCVendor advisory
  11. 2026-10-21 08:47 UTCGHSA enrichmentGHSA-92ww-hwmg-qq7p · GitHub severity HIGH · GitHub CVSS 8.2
  12. 2026-10-20 16:28 UTCEPSS rescoreEPSS 82% · 99th percentile
  13. 2026-10-18 08:51 UTCEG score recompute
  14. 2026-10-17 12:55 UTCOSV refresh
  15. 2026-10-15 16:28 UTCEPSS rescoreEPSS 82% · 99th percentile
  16. 2026-10-14 16:29 UTCEPSS rescoreEPSS 82% · 99th percentile
  17. 2026-10-12 19:07 UTCEG score recompute
  18. 2026-10-11 23:33 UTCEG score recompute
  19. 2026-10-09 20:04 UTCEPSS rescoreEPSS 82% · 99th percentile
  20. 2026-10-07 23:45 UTCEPSS rescoreEPSS 82% · 99th percentile
  21. 2026-10-05 17:40 UTCEPSS rescoreEPSS 82% · 99th percentile
  22. 2026-10-01 19:46 UTCEPSS rescoreEPSS 82% · 99th percentile
  23. 2026-09-30 15:43 UTCEG score recompute
  24. 2026-09-30 15:00 UTCEPSS rescoreEPSS 82% · 99th percentile
  25. 2026-09-28 13:47 UTCEPSS rescoreEPSS 82% · 99th percentile
Show 55 more
  1. 2026-09-25 10:06 UTCOSV refresh
  2. 2026-09-24 14:00 UTCEPSS rescoreEPSS 82% · 99th percentile
  3. 2026-09-22 14:44 UTCEPSS rescoreEPSS 82% · 99th percentile
  4. 2026-09-21 20:28 UTCEPSS rescoreEPSS 82% · 99th percentile
  5. 2026-09-18 19:23 UTCEPSS rescoreEPSS 82% · 99th percentile
  6. 2026-09-16 14:05 UTCEPSS rescoreEPSS 82% · 99th percentile
  7. 2026-09-12 14:57 UTCEPSS rescoreEPSS 82% · 99th percentile
  8. 2026-09-06 13:45 UTCEPSS rescoreEPSS 82% · 99th percentile
  9. 2026-09-06 01:30 UTCOSV refresh
  10. 2026-09-05 15:25 UTCEPSS rescoreEPSS 82% · 99th percentile
  11. 2026-09-04 05:03 UTCEPSS rescoreEPSS 82% · 99th percentile
  12. 2026-08-30 19:14 UTCEPSS rescoreEPSS 82% · 99th percentile
  13. 2026-08-30 01:19 UTCEPSS rescoreEPSS 82% · 99th percentile
  14. 2026-08-28 21:37 UTCEPSS rescoreEPSS 82% · 99th percentile
  15. 2026-08-26 14:43 UTCEPSS rescoreEPSS 82% · 99th percentile
  16. 2026-08-24 14:13 UTCEPSS rescoreEPSS 82% · 99th percentile
  17. 2026-08-20 22:52 UTCEPSS rescoreEPSS 82% · 99th percentile
  18. 2026-08-19 17:01 UTCEPSS rescoreEPSS 82% · 99th percentile
  19. 2026-08-19 12:59 UTCOSV refresh
  20. 2026-08-16 02:11 UTCEPSS rescoreEPSS 82% · 99th percentile
  21. 2026-08-15 01:27 UTCEPSS rescoreEPSS 82% · 99th percentile
  22. 2026-08-12 13:48 UTCEPSS rescoreEPSS 82% · 99th percentile
  23. 2026-08-06 13:44 UTCEPSS rescoreEPSS 82% · 99th percentile
  24. 2026-08-04 08:27 UTCOSV refresh
  25. 2026-07-28 15:33 UTCEPSS rescoreEPSS 82% · 99th percentile
  26. 2026-07-26 14:52 UTCEPSS rescoreEPSS 82% · 99th percentile
  27. 2026-07-24 14:15 UTCEPSS rescoreEPSS 82% · 99th percentile
  28. 2026-07-23 02:05 UTCEG score recompute▲ 0.80
  29. 2026-07-22 22:51 UTCEG score recompute
  30. 2026-07-22 14:06 UTCEPSS rescoreEPSS 82% · 99th percentile
  31. 2026-07-21 15:22 UTCEPSS rescoreEPSS 82% · 99th percentile
  32. 2026-07-20 17:05 UTCEPSS rescoreEPSS 82% · 99th percentile
  33. 2026-07-19 02:27 UTCEPSS rescoreEPSS 82% · 99th percentile
  34. 2026-07-18 05:29 UTCOSV refresh
  35. 2026-07-15 16:55 UTCEPSS rescoreEPSS 82% · 99th percentile
  36. 2026-07-13 22:27 UTCEPSS rescoreEPSS 82% · 99th percentile
  37. 2026-07-09 19:07 UTCEPSS rescoreEPSS 82% · 99th percentile
  38. 2026-07-06 16:25 UTCEPSS rescoreEPSS 82% · 99th percentile
  39. 2026-07-04 06:29 UTCEPSS rescoreEPSS 82% · 99th percentile
  40. 2026-07-01 15:04 UTCEPSS rescoreEPSS 82% · 99th percentile
  41. 2026-06-30 01:30 UTCOSV refresh
  42. 2026-06-28 04:54 UTCEPSS rescoreEPSS 82% · 99th percentile
  43. 2026-06-25 13:48 UTCEPSS rescoreEPSS 82% · 99th percentile
  44. 2026-06-23 21:31 UTCEPSS rescoreEPSS 82% · 99th percentile
  45. 2026-06-21 01:58 UTCEPSS rescoreEPSS 82% · 99th percentile
  46. 2026-06-17 17:51 UTCEPSS rescoreEPSS 82% · 99th percentile
  47. 2026-06-15 17:46 UTCEPSS rescoreEPSS 82% · 99th percentile
  48. 2026-06-14 23:15 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
  49. 2026-06-13 22:58 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
  50. 2026-06-12 23:10 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
  51. 2026-06-12 14:40 UTCOSV refresh
  52. 2026-06-11 13:58 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
  53. 2026-06-10 22:16 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
  54. 2026-06-10 13:20 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
  55. 2026-06-08 14:15 UTCEPSS rescoreEPSS 9.2% · 92nd percentile

Frequently asked(5)

What is CVE-2021-44224?
CVE-2021-44224 is a critical-severity vulnerability; its CVE record was published on December 20, 2021. A crafted URI sent to httpd configured as a forward proxy (ProxyRequests on) can cause a crash (NULL pointer dereference) or, for configurations mixing forward and reverse proxy declarations, can allow for requests to be directed to a declared Unix Domain Socket endpoint (Server Side Request…
When was the CVE record for CVE-2021-44224 published?
The CVE record for CVE-2021-44224 was published on December 20, 2021. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of November 21, 2024; the record at its source may have been updated since.
Is CVE-2021-44224 actively exploited?
CVE-2021-44224 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 82% probability of exploitation in the next 30 days (99th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-44224?
CVE-2021-44224 has a CVSS v3 base score of 8.2 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0 (CRITICAL).
How do I remediate CVE-2021-44224?
A fix for CVE-2021-44224 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-44224 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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