CVE-2021-40438 — Apache HTTP Server-Side Request Forgery (SSRF)

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

• Documented patch — www.oracle.com (NIST National Vulnerability Database)
• Documented patch — www.oracle.com (NIST National Vulnerability Database)

CISA required action CISA

Apply updates per vendor instructions.

US federal deadline: Dec 15, 2021 — passed 1765 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Apache Software Foundation Apache HTTP Server, Broadcom Brocade Fabric Operating System Firmware, Debian Debian Linux…).
2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
3. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
4. Apply the fixed version or the patch documented under Remediation.
5. EPSS ahead of 100% of scored CVEs: prioritize it in the patch queue.
6. Search available logs for exploit probes matching the vulnerability class (ssrf), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-918 · Server-Side Request Forgery (SSRF)

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 100.00%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
• Monitor outbound requests from the server to internal IPs and cloud metadata endpoints.
• Hunt retroactively in logs from before Dec 1, 2021 (KEV listing): exploitation may have started earlier.

Timeline

What happened to this CVE, newest first.

• 2026
• Affected products added · apache software foundation/apache http server
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• SSVC assessment updated
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Record published
  Oct 13, 2026
• Fix documented
  Oct 13, 2026 · NIST National Vulnerability Database
• Affected products added · resf/rocky linux, redhat/enterprise linux, redhat/enterprise linux eus, redhat/enterprise linux for arm 64, redhat/enter
  Oct 13, 2026 · NIST National Vulnerability Database
• CVSS changed · 9.0
  Oct 13, 2026 · NIST National Vulnerability Database
• Source status changed · → Analyzed
  Oct 13, 2026 · NIST National Vulnerability Database
• Added to CISA KEV (detected)
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• Record created in this database
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• 2021
• Added to CISA KEV catalog
  Nov 30, 2021 · CISA
• CVE published
  Sep 16, 2021 · apache

Source activity

Repeated readings are counted rather than listed.

• 2× References added · Oct 13, 2026 – Oct 13, 2026
• 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

34 on the record

• httpd.apache.org/security/vulnerabilities_24.html
  Release Notes, Vendor Advisory, x_refsource_MISC, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpuapr2022.html
  Patch, Third Party Advisory, x_refsource_MISC, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpujan2022.html
  Patch, Third Party Advisory, x_refsource_MISC, NIST National Vulnerability Database
• www.cisa.gov/known-exploited-vulnerabilities-catalog
  US Government Resource, NIST National Vulnerability Database
• lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCY
  Release Notes, vendor-advisory, x_refsource_FEDORA, NIST National Vulnerability Database
• nvd.nist.gov/vuln/detail/CVE-2021-40438
  GitHub Security Advisories
• lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZNCY
  GitHub Security Advisories
• lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029
  Mailing List, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• www.debian.org/security/2021/dsa-4982
  Mailing List, Third Party Advisory, vendor-advisory, x_refsource_DEBIAN, NIST National Vulnerability Database
• lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697
  GitHub Security Advisories
• tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2
  Broken Link, Third Party Advisory, vendor-advisory, x_refsource_CISCO, NIST National Vulnerability Database
• lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37
  GitHub Security Advisories
• lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00
  Mailing List, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432
  Mailing List, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• lists.debian.org/debian-lts-announce/2021/10/msg00001.html
  Mailing List, Third Party Advisory, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a
  GitHub Security Advisories
• security.netapp.com/advisory/ntap-20211008-0004/
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/SPBR6W
  GitHub Security Advisories
• lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR
  GitHub Security Advisories
• lists.apache.org/thread.html/r3925e167d5eb1c75def3750c155d753064e1d34a143028bb32910432
  GitHub Security Advisories
• github.com/advisories/GHSA-rwxq-58vm-3v2j
  GitHub Security Advisories
• security.gentoo.org/glsa/202208-20
  Third Party Advisory, vendor-advisory, x_refsource_GENTOO, NIST National Vulnerability Database
• lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c
  Mailing List, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SPBR
  Release Notes, vendor-advisory, x_refsource_FEDORA, NIST National Vulnerability Database
• lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ZNCYSR
  GitHub Security Advisories
• lists.apache.org/thread.html/r82c077663f9759c7df5a6656f925b3ee4f55fcd33c889ba7cd687029
  GitHub Security Advisories
• cert-portal.siemens.com/productcert/pdf/ssa-685781.pdf
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• lists.apache.org/thread.html/r61fdbfc26ab170f4e6492ef3bd5197c20b862ce156e9d5a54d4b899c
  GitHub Security Advisories
• lists.apache.org/thread.html/rf6954e60b1c8e480678ce3d02f61b8a788997785652e9557a3265c00
  GitHub Security Advisories
• lists.apache.org/thread.html/r210807d0bb55f4aa6fbe1512be6bcc4dacd64e84940429fba329967a
  Mailing List, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• lists.apache.org/thread.html/r2eb200ac1340f69aa22af61ab34780c531d110437910cb9c0ece3b37
  Mailing List, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• www.tenable.com/security/tns-2021-17
  Third Party Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
• lists.apache.org/thread.html/r82838efc5fa6fc4c73986399c9b71573589f78b31846aff5bd9b1697
  Mailing List, mailing-list, x_refsource_MLIST, NIST National Vulnerability Database
• security.netapp.com/advisory/ntap-20211008-0004
  GitHub Security Advisories

Elsewhere on this site

Related CVEs (same products)

• Medium CVE-2026-104046 Sssd: sssd: denial of service via incomplete identity provider authentication requests 9d
• Medium CVE-2026-104045 Sssd: sssd: denial of service via race condition in autofs responder 9d
• Medium CVE-2026-104047 Sssd: sssd: information disclosure via query injection in entra id lookups 9d
• High CVE-2026-104048 Sssd: sssd: authorization bypass via cross-domain username collision in hbac evaluation 9d
• High CVE-2026-102558 Libsoup: libsoup: heap buffer overflow during websocket receive-buffer growth 16d
• High CVE-2026-102555 Libsoup: libsoup: heap buffer overflow via uninitialized length in data-uri base64 decoding 16d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-40438 is "Apache HTTP Server-Side Request Forgery (SSRF)", rated Critical. It affects Apache HTTP Server (Apache Software Foundation); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 9.0 describes technical severity. EPSS 100.00% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.

Sign in or create an account to comment and suggest corrections.