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    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. This issue affects Apache HTTP Server 2.4.48 and earlier.

    Published:Sep 16, 2021
    Last Modified:Aug 5, 2026
    EPS:Sep 16, 2021
    EPSS Score:0.99999
    CVSS Score:9

    CISA Notification

    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.

    Required Action:

    Apply updates per vendor instructions.

    Notes:

    No extra notes provided.

    Due Date
    Dec 15, 2021
    1731 days ago
    Alert Date
    Dec 1, 2021
    1745 days ago

    Affected Products

    Vendor
    Apache
    Product
    Http Server
    Vendor
    Broadcom
    Product
    Brocade Fabric Operating System Firmware
    Vendor
    Debian
    Product
    Debian Linux
    Vendor
    F5
    Product
    F5os
    Vendor
    Fedoraproject
    Product
    Fedora
    Vendor
    Netapp
    Product
    Cloud Backup
    Vendor
    Netapp
    Product
    Clustered Data Ontap
    Vendor
    Netapp
    Product
    Storagegrid
    Vendor
    Oracle
    Product
    Enterprise Manager Ops Center
    Vendor
    Oracle
    Product
    Http Server
    Vendor
    Oracle
    Product
    Instantis Enterprisetrack
    Vendor
    Oracle
    Product
    Secure Global Desktop
    Vendor
    Oracle
    Product
    Zfs Storage Appliance Kit
    Vendor
    Redhat
    Product
    Enterprise Linux
    Vendor
    Redhat
    Product
    Enterprise Linux Eus
    Vendor
    Redhat
    Product
    Enterprise Linux For Arm 64
    Vendor
    Redhat
    Product
    Enterprise Linux For Arm 64 Eus
    Vendor
    Redhat
    Product
    Enterprise Linux For Ibm Z Systems
    Vendor
    Redhat
    Product
    Enterprise Linux For Ibm Z Systems Eus
    Vendor
    Redhat
    Product
    Enterprise Linux For Ibm Z Systems Eus S390x
    Vendor
    Redhat
    Product
    Enterprise Linux For Power Big Endian
    Vendor
    Redhat
    Product
    Enterprise Linux For Power Little Endian
    Vendor
    Redhat
    Product
    Enterprise Linux For Power Little Endian Eus
    Vendor
    Redhat
    Product
    Enterprise Linux For Scientific Computing
    Vendor
    Redhat
    Product
    Enterprise Linux Server
    Vendor
    Redhat
    Product
    Enterprise Linux Server Aus
    Vendor
    Redhat
    Product
    Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions
    Vendor
    Redhat
    Product
    Enterprise Linux Server Tus
    Vendor
    Redhat
    Product
    Enterprise Linux Server Update Services For Sap Solutions
    Vendor
    Redhat
    Product
    Enterprise Linux Server Workstation
    Vendor
    Redhat
    Product
    Enterprise Linux Update Services For Sap Solutions
    Vendor
    Redhat
    Product
    Enterprise Linux Workstation
    Vendor
    Redhat
    Product
    Jboss Core Services
    Vendor
    Redhat
    Product
    Rhel Aus
    Vendor
    Redhat
    Product
    Rhel E4s
    Vendor
    Redhat
    Product
    Rhel Eus
    Vendor
    Redhat
    Product
    Rhel Software Collections
    Vendor
    Redhat
    Product
    Rhel Tus
    Vendor
    Redhat
    Product
    Software Collections
    Vendor
    Resf
    Product
    Rocky Linux
    Vendor
    Siemens
    Product
    Ruggedcom Nms
    Vendor
    Siemens
    Product
    Sinec Nms
    Vendor
    Siemens
    Product
    Sinema Remote Connect Server
    Vendor
    Siemens
    Product
    Sinema Server
    Vendor
    Tenable
    Product
    Tenable.sc

    Exploits

    https://github.com/BabyTeam1024/CVE-2021-40438https://github.com/Cappricio-Securities/CVE-2021-40438https://github.com/ericmann/apache-cve-pochttps://github.com/gassara-kys/CVE-2021-40438https://github.com/Kashkovsky/CVE-2021-40438https://github.com/n0m-d/CVE-2021-40438-POChttps://github.com/pisut4152/Sigma-Rule-for-CVE-2021-40438-exploitation-attempthttps://github.com/sergiovks/CVE-2021-40438-Apache-2.4.48-SSRF-exploithttps://github.com/sixpacksecurity/CVE-2021-40438https://github.com/xiaojiangxl/CVE-2021-40438https://github.com/yakir2b/check-point-gateways-rce

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-664 Server Side Request Forgery

    Related CVEs

    CVE-2026-48913 (CVSS 7.3) — Use After Free vulnerability in Apache HTTP Server module mod_http2 when file handles are already exhausted. …
    CVE-2026-42536 (CVSS 7.5) — Heap-based Buffer Overflow vulnerability in Apache HTTP Server with mod_xml2enc, xml2StartParse, and untrusted…
    CVE-2026-44185 (CVSS 7.3) — Buffer Over-read vulnerability in Apache HTTP Server via outbound OCSP requests to an attacker controlled OCSP…
    CVE-2026-34355 (CVSS 7.5) — A buffer overflow in mod_proxy_html in Apache HTTP Server 2.4.67 and earlier allows an attack by an untrusted …
    CVE-2026-44631 (CVSS 9.8) — Buffer Underwrite vulnerability in Apache HTTP Server on crafted regular expressions in the configuration. Th…
    CVE-2026-44119 (CVSS 5.5) — Improper Privilege Management vulnerability in Apache HTTP Server 2.4.67 and earlier allows local .htaccess au…
    CVE-2026-43951 (CVSS 6.5) — Out-of-bounds Read vulnerability in Apache HTTP Server with mod_headers and mod_mime and multiple response lan…
    CVE-2026-42535 (CVSS 9.1) — A path handling issue in mod_dav_fs in Apache 2.4.67 and earlier allows a WebDAV content author to directly ma…
    CVE-2026-34356 (CVSS 7.5) — Heap-based Buffer Overflow vulnerability in Apache HTTP Server with malicious backend servers and ProxyPassRev…
    CVE-2026-44186 (CVSS 7.3) — Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in the mod_proxy_ftp module in Apache HTT…

    References

    https://cert-portal.siemens.com/productcert/pdf/ssa-685781.pdf
    https://httpd.apache.org/security/vulnerabilities_24.html
    https://lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3E
    https://lists.debian.org/debian-lts-announce/2021/10/msg00001.html
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7TJOHX7RHWD/
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3HDQK4VP45R/
    https://security.gentoo.org/glsa/202208-20
    https://security.netapp.com/advisory/ntap-20211008-0004/
    https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ
    https://www.debian.org/security/2021/dsa-4982
    https://www.oracle.com/security-alerts/cpuapr2022.html
    https://www.oracle.com/security-alerts/cpujan2022.html
    https://www.tenable.com/security/tns-2021-17
    https://cert-portal.siemens.com/productcert/pdf/ssa-685781.pdf
    https://httpd.apache.org/security/vulnerabilities_24.html
    https://lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37%40%3Cbugs.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029%40%3Cusers.httpd.apache.org%3E
    https://lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00%40%3Cusers.httpd.apache.org%3E
    https://lists.debian.org/debian-lts-announce/2021/10/msg00001.html
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR6WUYBJNACHKE65SPL7TJOHX7RHWD/
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCYSR3BXT36FFF4XTCPL3HDQK4VP45R/
    https://security.gentoo.org/glsa/202208-20
    https://security.netapp.com/advisory/ntap-20211008-0004/
    https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ
    https://www.debian.org/security/2021/dsa-4982
    https://www.oracle.com/security-alerts/cpuapr2022.html
    https://www.oracle.com/security-alerts/cpujan2022.html
    https://www.tenable.com/security/tns-2021-17
    https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40438

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High