CVE-2021-40438
KEVRansomware UseApache HTTP Server-Side Request Forgery (SSRF)
Description
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.
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.
CVSS 3.1 vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:HPublishedSep 16, 2021
Last modifiedAug 6, 2026
Added to KEVDec 1, 2021
Remediation dueDec 15, 2021
References
- cert-portal.siemens.com/productcert/pdf/ssa-685781.pdfThird Party Advisory
- httpd.apache.org/security/vulnerabilities_24.htmlRelease NotesVendor Advisory
- lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3EMailing List
- lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3EMailing List
- lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3EMailing List
- lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3EMailing List
- lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3EMailing List
- lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3EMailing List
- lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3EMailing List
- lists.debian.org/debian-lts-announce/2021/10/msg00001.htmlMailing ListThird Party Advisory
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7TJOHX7RHWD/Release Notes
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3HDQK4VP45R/Release Notes
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95
Risk assessment · Critical
Actively exploited and used by ransomware crews. Patch immediately.
- Exploitation
- Confirmed in the wild (CISA KEV)
- Federal remediation deadline
- Overdue by 1776 days
- Ransomware
- Used in known ransomware campaigns
- CVSS
- 9.0 CRITICAL
- EPSS (30-day exploit probability)
- 100.0% · top 1% of all CVEs
- Weakness
- CWE-918
- Attack vector
- Network, remotely reachable
- Preconditions
- No privileges and no user interaction
Recommended actions
- 1.Apply updates per vendor instructions.
- 2.Treat as emergency change: patch or isolate internet-facing instances first.
- 3.Review exposure: confirm which instances are reachable from the internet and restrict access until patched.
- 4.Hunt for compromise: review logs for the disclosure window, not just from the patch date.
- 5.Verify offline/immutable backups and segment the affected systems. This flaw is used for ransomware initial access.
Assessment is derived automatically from the live signals above; verify against your own asset inventory.