Apache · Apache
CVE-2021-40438
mod_proxy SSRF
Exploited in attacks
Used by ransomware
Critical 9.0 Attack chance: >99.9%
What it is
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.
What to do
Apply updates per vendor instructions.
Deadline for US federal agencies: December 15, 2021
- Added to the CISA list
- December 1, 2021
- Published
- September 16, 2021
- Severity
- Critical 9.0 CVSS 3.1
- Chance of attacks in the next 30 days (EPSS)
- >99.9% in the top 0.1% of all known vulnerabilities
- Weakness
- CWE-918
- More details
- NVD · CVE.org · CISA
All references (19)
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNA…
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36…
- https://www.debian.org/security/2021/dsa-4982
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ
- https://security.gentoo.org/glsa/202208-20
- https://httpd.apache.org/security/vulnerabilities_24.html
- https://lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.htt…
- https://lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.htt…
- https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.htt…
- https://lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.htt…
- https://lists.debian.org/debian-lts-announce/2021/10/msg00001.html
- https://lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.http…
- https://lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.htt…
- https://lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.htt…
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.tenable.com/security/tns-2021-17
- https://security.netapp.com/advisory/ntap-20211008-0004/
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-685781.pdf
More exploited flaws from Apache
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| Oct 8, 2026 | Command Injection | Struts | High 8.1 | 97% |
| Aug 4, 2026 | Missing Encryption of Sensitive Data | Tomcat | High 7.5 | 99% |
| Apr 16, 2026 | Improper Input Validation | ActiveMQ | High 8.8 | 98% |
| May 1, 2025 | Improper Escaping of Output | HTTP Server | Critical 9.1 | >99.9% |
| Apr 1, 2025 | Path Equivalence | Tomcat | Critical 10.0 | 99.9% |
| Feb 4, 2025 | Forced Browsing | OFBiz | Critical 9.8 | >99.9% |
| Sep 18, 2024 | Improper Access Control | HugeGraph-Server | Critical 9.8 | 99.2% |
| Aug 27, 2024 | Incorrect Authorization | OFBiz | High 8.1 | 99.4% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.