CVE-2021-40438
CriticalPublished
mod_proxy SSRF
- Published
- Sep 16, 2021
- Updated
- Aug 6, 2026
- Assigning CNA
- apache
- Evidence observed
- Dec 1, 2021
Primary CVSS
9.0/ 10Critical
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H100.0%
High · next 30 days
- Percentile
- 100.0%
- Model date
- Oct 17, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
CISA Known Exploited
This CVE appears in the CISA Known Exploited Vulnerabilities catalog.
Summary
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.
Sources
Repository evidence: Files: 2 · Repositories: 2
1 Template1 Lab
httpd/CVE-2021-40438
Apache HTTP Server 2.4.48 mod_proxy SSRF (CVE-2021-40438)
Vulhub vulnerability labsDeclared conditions
- lab image version: vulhub/tomcat:8.5.19(httpd/CVE-2021-40438/docker-compose.yml:services.tomcat.image)
http/cves/2021/CVE-2021-40438.yaml
Nuclei TemplatesDeclared conditions
- network: http($.protocol_keys)
- verification: dsl($.matchers[*].type)
- oob: interactsh_reference($.template_text)
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