CVE-2021-40438: A crafted request uri-path can cause mod_proxy to forward the request to an origin server choosen by the remote user.
Noroxi assessment
Priority: Now (action score 96/100)
- CISA has confirmed exploitation in the wild (Dec 1, 2021); it is known to be used in ransomware campaigns. Remediation deadline for US federal agencies: Dec 15, 2021.
- A ready-made attack module is public (Nuclei); exploiting it takes no special expertise.
- Probability of exploitation in the next 30 days: 99.9% (FIRST EPSS); higher than 99.9% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- Fixed version: httpd (AlmaLinux:8) 2.4.37-43.module_el8.5.0+2597+c4b14997.alma; httpd-devel (AlmaLinux:8) 2.4.37-43.module_el8.5.0+2597+c4b14997.alma; httpd-filesystem (AlmaLinux:8) 2.4.37-43.module_el8.5.0+2597+c4b14997.alma.
- Mentioned 6 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).
Patch today or shut off access. Upgrade to httpd (AlmaLinux:8) 2.4.37-43.module_el8.5.0+2597+c4b14997.alma; httpd-devel (AlmaLinux:8) 2.4.37-43.module_el8.5.0+2597+c4b14997.alma; httpd-filesystem (AlmaLinux:8) 2.4.37-43.module_el8.5.0+2597+c4b14997.alma or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · CISA KEV · FIRST EPSS
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.
- BDU:2021-04820
- ALBA-2021:4604
- ALSA-2021:3816
- ALSA-2021:4537
- DLA-2776-1
- DSA-4982-1
- openSUSE-SU-2021:1438-1
- openSUSE-SU-2021:3522-1
- openSUSE-SU-2025:14708-1
- RHSA-2021:3746
- RHSA-2021:3754
- RHSA-2021:3816
- RHSA-2021:3836
- RHSA-2021:3837
- RHSA-2021:3856
- RLSA-2021:3816
- SUSE-SU-2021:3299-1
- SUSE-SU-2021:3335-1
- SUSE-SU-2021:3522-1
- Published
- Sep 16, 2021
- Updated
- Aug 6, 2026
- EPSS
- 99.9% · 99th percentile
- CWE
- CWE-918
Report tools
Action score
96
Now
Patch today or shut off access.
- CVSS
- 36 / 40 · 9.0 / 10
- CISA KEV
- 30 / 30 · Listed
- EPSS
- 30 / 30 · 99.9%
CISA SSVC decision
- Exploitation
- active
- Automatable
- yes
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
Actively exploited in the wild
CISA added this to its Known Exploited Vulnerabilities catalog on Dec 1, 2021. That signals real attacks, not theory.
Remediation deadline for US federal agencies: Dec 15, 2021.
Known to be used in ransomware campaigns.
Get told when this record changes
- In CISA KEV: exploitation in the wild confirmed
- Weaponized exploit exists
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| resf | rocky linux | cpe:2.3:o:resf:rocky_linux |
| redhat | enterprise linux | cpe:2.3:o:redhat:enterprise_linux |
| redhat | enterprise linux eus | cpe:2.3:o:redhat:enterprise_linux_eus |
| redhat | enterprise linux for arm 64 | cpe:2.3:o:redhat:enterprise_linux_for_arm_64 |
| redhat | enterprise linux for arm 64 eus | cpe:2.3:o:redhat:enterprise_linux_for_arm_64_eus |
| redhat | enterprise linux for ibm z systems | cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems |
| redhat | enterprise linux for ibm z systems eus | cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems_eus |
| redhat | enterprise linux for ibm z systems eus s390x | cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems_eus_s390x |
| redhat | enterprise linux for power big endian | cpe:2.3:o:redhat:enterprise_linux_for_power_big_endian |
| redhat | enterprise linux for power little endian | cpe:2.3:o:redhat:enterprise_linux_for_power_little_endian |
| redhat | enterprise linux for power little endian eus | cpe:2.3:o:redhat:enterprise_linux_for_power_little_endian_eus |
| redhat | enterprise linux for scientific computing | cpe:2.3:o:redhat:enterprise_linux_for_scientific_computing |
and 28 more
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- apache http serverup to 2.4.48 inclusive
Versions reported by the vendor
Affected version ranges reported by the assigning authority (apache). Independent of NVD's CPE analysis and usually ahead of it.
Apache Software Foundation Apache HTTP Server
- Apache HTTP Server 2.4 and later · up to and including 2.4.48affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| AlmaLinux:8 | httpd | before 2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | httpd-devel | before 2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | httpd-filesystem | before 2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | httpd-manual | before 2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | httpd-tools | before 2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | mod_http2 | before 1.15.7-3.module_el8.5.0+2609+b30d9eec | 1.15.7-3.module_el8.5.0+2609+b30d9eec |
| AlmaLinux:8 | mod_ldap | before 2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | mod_md | before 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa | 1:2.0.8-8.module_el8.6.0+2872+fe0ff7aa |
| AlmaLinux:8 | mod_md | before 1:2.0.8-8.module_el8.5.0+2609+b30d9eec | 1:2.0.8-8.module_el8.5.0+2609+b30d9eec |
| AlmaLinux:8 | mod_proxy_html | before 1:2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 1:2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | mod_session | before 2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| AlmaLinux:8 | mod_ssl | before 1:2.4.37-43.module_el8.5.0+2597+c4b14997.alma | 1:2.4.37-43.module_el8.5.0+2597+c4b14997.alma |
| Alpine:v3.11 | apache2 | before 2.4.49-r0 | 2.4.49-r0 |
| Debian:10 | apache2 | before 2.4.38-3+deb10u6 | 2.4.38-3+deb10u6 |
| Debian:11 | apache2 | before 2.4.51-1~deb11u1 | 2.4.51-1~deb11u1 |
| Debian:12 | apache2 | before 2.4.49-1 | 2.4.49-1 |
| Debian:9 | apache2 | before 2.4.25-3+deb9u11 | 2.4.25-3+deb9u11 |
| openSUSE:Leap 15.2 | apache2 | before 2.4.43-lp152.2.21.1 | 2.4.43-lp152.2.21.1 |
| openSUSE:Leap 15.3 | apache2 | before 2.4.43-3.32.1 | 2.4.43-3.32.1 |
| openSUSE:Tumbleweed | owasp-modsecurity-crs | before 4.9.0-1.1 | 4.9.0-1.1 |
| Red Hat:enterprise_linux:7::client | httpd | before 0:2.4.6-97.el7_9.1 | 0:2.4.6-97.el7_9.1 |
| Red Hat:enterprise_linux:7::client | httpd-debuginfo | before 0:2.4.6-97.el7_9.1 | 0:2.4.6-97.el7_9.1 |
| Red Hat:enterprise_linux:7::client | httpd-devel | before 0:2.4.6-97.el7_9.1 | 0:2.4.6-97.el7_9.1 |
| Red Hat:enterprise_linux:7::client | httpd-manual | before 0:2.4.6-97.el7_9.1 | 0:2.4.6-97.el7_9.1 |
+96
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| almalinux:httpd | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-devel | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-filesystem | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-manual | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:httpd-tools | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_http2 | 1.15.7-3.module_el8.5.0+2609+b30d9eec · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_ldap | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_md | 1:2.0.8-8.module_el8.5.0+2609+b30d9eec · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_proxy_html | 1:2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_session | 2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| almalinux:mod_ssl | 1:2.4.37-43.module_el8.5.0+2597+c4b14997.alma · AlmaLinux:8 | Package registry (OSV) |
| alpine:apache2 | 2.4.49-r0 · Alpine:v3.11 | Package registry (OSV) |
| debian:apache2 | 2.4.49-1 · Debian:12 | Package registry (OSV) |
| opensuse:apache2 | 2.4.43-lp152.2.21.1 · openSUSE:Leap 15.2 | Package registry (OSV) |
| opensuse:owasp-modsecurity-crs | 4.9.0-1.1 · openSUSE:Tumbleweed | Package registry (OSV) |
| red hat:jbcs-httpd24-httpd | 0:2.4.37-76.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-httpd-debuginfo | 0:2.4.37-76.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-httpd-devel | 0:2.4.37-76.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-httpd-manual | 0:2.4.37-76.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-httpd-selinux | 0:2.4.37-76.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-httpd-tools | 0:2.4.37-76.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-mod_cluster-native | 0:1.3.16-7.Final_redhat_2.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-mod_cluster-native-debuginfo | 0:1.3.16-7.Final_redhat_2.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-mod_http2 | 0:1.15.7-19.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-mod_http2-debuginfo | 0:1.15.7-19.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-mod_jk | 0:1.2.48-18.redhat_1.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| red hat:jbcs-httpd24-mod_jk-ap24 | 0:1.2.48-18.redhat_1.jbcs.el7 · Red Hat:jboss_core_services:1::el7 | Package registry (OSV) |
| rocky linux:httpd | 0:2.4.37-39.module+el8.4.0+571+fd70afb1 · Rocky Linux:8 | Package registry (OSV) |
| rocky linux:mod_http2 | 0:1.15.7-3.module+el8.4.0+553+7a69454b · Rocky Linux:8 | Package registry (OSV) |
| rocky linux:mod_md | 1:2.0.8-8.module+el8.5.0+695+1fa8055e · Rocky Linux:8 | Package registry (OSV) |
+1
Exploit status
Weaponized
A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.
Evidence
- Nuclei detection template ×1
- Proof-of-concept repository on GitHub ×11
Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.
| Source | Kind | Date |
|---|---|---|
| Nuclei detection template | Nuclei template CVE-2021-40438 | — |
| Proof-of-concept repository on GitHub | stars:5 | 2021-10-18 |
| Proof-of-concept repository on GitHub | stars:13 | 2021-10-24 |
| Proof-of-concept repository on GitHub | stars:2 | 2021-10-28 |
| Proof-of-concept repository on GitHub | stars:0 | 2021-11-11 |
| Proof-of-concept repository on GitHub | stars:1 | 2021-11-30 |
| Proof-of-concept repository on GitHub | stars:18 | 2022-04-03 |
| Proof-of-concept repository on GitHub | stars:1 | 2022-06-10 |
| Proof-of-concept repository on GitHub | stars:11 | 2023-12-12 |
| Proof-of-concept repository on GitHub | stars:1 | 2024-05-19 |
| Proof-of-concept repository on GitHub | stars:0 | 2025-01-22 |
| Proof-of-concept repository on GitHub | stars:0 | 2025-11-09 |
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Published
- First PoC+32 d
- CISA KEV+76 d
- TodayNov 3, 2026+1874 d
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
National notice (Türkiye Cybersecurity Directorate / USOM)
Official security notices citing this record; remediation advice is on the agency's page.
- TR-22-0596 · Sep 8, 2022(IBM Güvenlik Zafiyeti)
- TR-21-0956 · Nov 30, 2021(Apache HTTP Server Zafiyeti)
- TR-21-0952 · Nov 30, 2021(Cisco Güvenlik Zafiyeti)
- TR-21-0947 · Nov 25, 2021(Cisco Güvenlik Zafiyeti)
- TR-21-0848 · Oct 19, 2021(RedHat Güvenlik Güncellemesi)
- TR-21-0824 · Oct 12, 2021(RedHat Güvenlik Güncellemesi)
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- high · the service can be disrupted
Impact can extend beyond the vulnerable component (scope changes).
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
CWE-918 · Server-Side Request Forgery (SSRF)CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
—
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (19 more)Show less
- httpd.apache.org/security/vulnerabilities_24.html
- lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E
- lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E
- lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E
- lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E
- lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E
- lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E
- lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3E
- lists.debian.org/debian-lts-announce/2021/10/msg00001.html
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7TJOHX7RHWD/
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3HDQK4VP45R/
- security.gentoo.org/glsa/202208-20
- security.netapp.com/advisory/ntap-20211008-0004/
- tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ
- www.debian.org/security/2021/dsa-4982
- www.oracle.com/security-alerts/cpuapr2022.html
- www.oracle.com/security-alerts/cpujan2022.html
- www.tenable.com/security/tns-2021-17
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40438
Vendor advisories and official records. Exploit/PoC links are deliberately left out.