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).
CVE-2021-44224
“▲” 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.
- 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%
A fix is available — apply it.
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.
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
- 70EG 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, 2026Apache HTTPD: Multiple Vulnerabilities (GLSA 202208-20) — Gentoo security
https://security.gentoo.org/glsa/202208-20[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/[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/[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/[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/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/2021/12/20/3Full Disclosure: APPLE-SA-2022-05-16-2 macOS Monterey 12.4
http://seclists.org/fulldisclosure/2022/May/38Full Disclosure: APPLE-SA-2022-05-16-3 macOS Big Sur 11.6.6
http://seclists.org/fulldisclosure/2022/May/35Full Disclosure: APPLE-SA-2022-05-16-4 Security Update 2022-004 Catalina
http://seclists.org/fulldisclosure/2022/May/33Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project
http://httpd.apache.org/security/vulnerabilities_24.htmlVendor Advisories for CVE-2021-44224(3)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2022:7144Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat JBoss Core Services Apache HTTP Server 2.4.51 security update
- RHSA-2022:6753Red Hat Product SecurityMedium
Red Hat Security Advisory: httpd24-httpd security and bug fix update
- CVE-2021-44224Microsoft Security Response Center (MSRC)High
Possible NULL dereference or SSRF in forward proxy configurations in Apache HTTP Server 2.4.51 and earlier
Patch Availability(6)
| Vendor / Ecosystem | Fix (by version range) / Patch | Released | Source |
|---|---|---|---|
| ubuntu | apache2-bin (2.4.48-3.1ubuntu3.2) @ impish | 2026-10-22 | ubuntu |
| ubuntu | apache2-utils (2.4.18-2ubuntu3.17+esm4) @ xenial | 2026-10-22 | ubuntu |
| redhat | jbcs-httpd24-httpd | 2022-10-26 | redhat |
| redhat | jbcs-httpd24-httpd-0:2.4.51-28.el7jbcs | 2022-10-26 | redhat |
| redhat | httpd24-httpd-0:2.4.34-23.el7.5 | 2022-09-29 | redhat |
| redhat | httpd:2.4-8060020220321163517.d63f516d | 2022-05-10 | redhat |
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)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.15(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.16(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.17(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.18(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.19(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.20(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.21(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.22(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.23(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Alpine:v3.24(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Debian:10(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | 2.4.38-3 ... 2.4.38-3+deb10u6 (7 versions) |
| — |
Debian:11(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | 2.4.48-3.1 ... 2.4.52-1~deb11u1 (20 versions) |
| — |
Debian:12(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Debian:13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | — |
| — |
Debian:9(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| apache2 | 2.4.25-3 ... 2.4.25-3+deb9u9 (12 versions) |
| — |
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.
- 2026-10-23 05:33 UTCEG score recompute
- 2026-10-23 05:33 UTCVendor advisory
- 2026-10-23 05:33 UTCGHSA enrichmentGHSA-92ww-hwmg-qq7p · GitHub severity HIGH · GitHub CVSS 8.2
- 2026-10-22 16:29 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-22 07:09 UTCEG score recompute
- 2026-10-22 07:09 UTCVendor advisory
- 2026-10-22 07:09 UTCGHSA enrichmentGHSA-92ww-hwmg-qq7p · GitHub severity HIGH · GitHub CVSS 8.2
- 2026-10-21 16:28 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-21 08:47 UTCEG score recompute
- 2026-10-21 08:47 UTCVendor advisory
- 2026-10-21 08:47 UTCGHSA enrichmentGHSA-92ww-hwmg-qq7p · GitHub severity HIGH · GitHub CVSS 8.2
- 2026-10-20 16:28 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-18 08:51 UTCEG score recompute
- 2026-10-17 12:55 UTCOSV refresh
- 2026-10-15 16:28 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-14 16:29 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-12 19:07 UTCEG score recompute
- 2026-10-11 23:33 UTCEG score recompute
- 2026-10-09 20:04 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-07 23:45 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-05 17:40 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-10-01 19:46 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-30 15:43 UTCEG score recompute
- 2026-09-30 15:00 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-28 13:47 UTCEPSS rescoreEPSS 82% · 99th percentile
Show 55 moreShow fewer
- 2026-09-25 10:06 UTCOSV refresh
- 2026-09-24 14:00 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-22 14:44 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-21 20:28 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-18 19:23 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-16 14:05 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-12 14:57 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-06 13:45 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-06 01:30 UTCOSV refresh
- 2026-09-05 15:25 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-09-04 05:03 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-30 19:14 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-30 01:19 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-28 21:37 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-26 14:43 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-24 14:13 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-20 22:52 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-19 17:01 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-19 12:59 UTCOSV refresh
- 2026-08-16 02:11 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-15 01:27 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-12 13:48 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-06 13:44 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-08-04 08:27 UTCOSV refresh
- 2026-07-28 15:33 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-26 14:52 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-24 14:15 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-23 02:05 UTCEG score recompute▲ 0.80
- 2026-07-22 22:51 UTCEG score recompute
- 2026-07-22 14:06 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-21 15:22 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-20 17:05 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-19 02:27 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-18 05:29 UTCOSV refresh
- 2026-07-15 16:55 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-13 22:27 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-09 19:07 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-06 16:25 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-04 06:29 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-07-01 15:04 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-06-30 01:30 UTCOSV refresh
- 2026-06-28 04:54 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-06-25 13:48 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-06-23 21:31 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-06-21 01:58 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-06-17 17:51 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-06-15 17:46 UTCEPSS rescoreEPSS 82% · 99th percentile
- 2026-06-14 23:15 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
- 2026-06-13 22:58 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
- 2026-06-12 23:10 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
- 2026-06-12 14:40 UTCOSV refresh
- 2026-06-11 13:58 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
- 2026-06-10 22:16 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
- 2026-06-10 13:20 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
- 2026-06-08 14:15 UTCEPSS rescoreEPSS 9.2% · 92nd percentile
Related CVEs(same product + same vendor + same CWE)
Same product
10 shownDebian:10:apache2
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- CVE-2021-39275EG 9.8EPSS p99CRITICAL
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- CVE-2019-10082EG 9.1EPSS p97CRITICAL
- CVE-2021-40438EG 9.0 KEVEPSS p100CRITICAL
- CVE-2019-10092NVD 6.1EG 8.8EPSS p100HIGH
- CVE-2021-26690NVD 7.5EG 8.5EPSS p99HIGH
- CVE-2021-34798NVD 7.5EG 8.4EPSS p99HIGH
- CVE-2019-10098NVD 6.1EG 8.4EPSS p99HIGH
- CVE-2021-31618NVD 7.5EG 8.1EPSS p99HIGH
Same vendor
10 shownredhat:RHSA-2022:1915 · redhat:RHSA-2022:6753 · ubuntu:USN-5212-1
- CVE-2021-36160NVD 7.5EG 8.4EPSS p99HIGH
- CVE-2021-33193NVD 7.5EG 7.9EPSS p99HIGH
- CVE-2021-39275EG 9.8EPSS p99CRITICAL
- CVE-2021-44790EG 9.8EPSS p100CRITICAL
- CVE-2021-41524EG 7.5EPSS p98HIGH
- CVE-2022-31813EG 9.8CRITICAL
- CVE-2022-23943EG 9.8EPSS p99CRITICAL
- CVE-2022-22721NVD 9.1EG 9.8EPSS p99CRITICAL
- CVE-2022-25315EG 9.8EPSS p92CRITICAL
- CVE-2022-25236EG 9.8EPSS p98CRITICAL
Frequently asked(5)
What is CVE-2021-44224?
When was the CVE record for CVE-2021-44224 published?
Is CVE-2021-44224 actively exploited?
What is the CVSS score of CVE-2021-44224?
How do I remediate CVE-2021-44224?
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-44224
Is Your Infrastructure Affected by CVE-2021-44224?
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