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PatchSiren cyber security CVE debrief

CVE-2021-40438 Apache CVE debrief

CVE-2021-40438 is an Apache HTTP Server server-side request forgery (SSRF) issue that CISA added to its Known Exploited Vulnerabilities catalog on 2021-12-01. Because it is listed in KEV, organizations should treat remediation as urgent and follow the vendor’s update guidance promptly.

Vendor
Apache
Product
Apache
CVSS
CRITICAL 9
CISA KEV
Listed
Original CVE published
2021-12-01
Original CVE updated
2021-12-01
Advisory published
2021-12-01
Advisory updated
2021-12-01

Who should care

Apache HTTP Server administrators, platform and infrastructure teams, vulnerability management owners, and anyone running exposed Apache services should prioritize this CVE.

Technical summary

The supplied source corpus identifies this issue as an SSRF affecting Apache HTTP Server. The strongest defensive signal in the corpus is CISA’s KEV entry, which indicates the vulnerability is known to be exploited and should be remediated by applying updates per vendor instructions.

Defensive priority

Urgent. KEV-listed vulnerabilities should be prioritized ahead of routine maintenance, especially on internet-facing or broadly reachable Apache HTTP Server deployments. CISA’s due date in the supplied timeline is 2021-12-15.

Recommended defensive actions

  • Inventory Apache HTTP Server deployments to confirm exposure and ownership.
  • Check the official Apache and NVD records for vendor-directed remediation guidance.
  • Apply the recommended Apache updates or mitigations as soon as possible.
  • Prioritize internet-facing and externally reachable systems first.
  • Verify remediation after patching and confirm the vulnerable version is no longer present.
  • Review relevant logs for unusual server-initiated or outbound request patterns that could indicate abuse.

Evidence notes

This debrief is intentionally limited to the supplied corpus and official links. The source material identifies the CVE as an Apache HTTP Server SSRF issue and places it in CISA’s Known Exploited Vulnerabilities catalog with a remediation instruction to apply updates per vendor guidance. No additional version ranges, attack details, or exploit mechanics were introduced beyond the supplied evidence.

Sources and references

Verified primary and authoritative sources

  • CVE-2021-40438 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2021-40438

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2021-40438 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2021-40438

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

  • CISA Known Exploited Vulnerabilities catalog

    Publisher, destination, and source semantics verified

    URL: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

    Cybersecurity and Infrastructure Security Agency - Official CISA catalog of vulnerabilities known to be exploited in the wild.

Supplemental references

  • Source item URL

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

    cisa_kev

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.