Yes. CISA added CVE-2021-41773 to its Known Exploited Vulnerabilities catalogue on 3 November 2021, which it does only when there is reliable evidence of active exploitation. CISA lists it as known to be used in ransomware campaigns. Apache HTTP Server contains a path traversal vulnerability that allows an attacker to perform remote code execution if files outside directories configured by Alias-like directives are not under default �require all denied� or if CGI scripts are enabled.
How to Tell Whether This CVE Is Actively Exploited
The practical test is not whether the flaw exists, but whether there is credible evidence that attackers are already using it against exposed systems. For this CVE, that means checking CISA KEV status, the vendor advisory, and any signs that your Apache HTTP Server deployment could be reachable through the vulnerable path traversal condition described in the direct answer.
For internet-facing web servers, the exposure question is often more important than the software name alone. If the server exposes the affected content paths or CGI execution paths, the issue is not theoretical. If you need a broader operating model for separating discovered flaws from actively exploited ones, use the Zero-Day and Exploited Vulnerabilities Guide to anchor triage on KEV status, exploitability, and emergency response timing.
Because this is a path traversal issue that can escalate to remote code execution in some configurations, the key operational question is whether your deployment actually allows requests to escape intended document roots or invoke CGI in a dangerous way. If the answer is yes, treat the system as exposed until proven otherwise.
What Exploitation Looks Like in Practice
In real incidents, exploitation of path traversal flaws usually starts with simple request manipulation and then moves to file discovery, script execution, or staging of follow-on payloads. Attackers do not need novel tradecraft if the server is already misconfigured or reachable with unsafe defaults.
That makes this class of bug easy to weaponise at scale. Automated scanners can probe for the vulnerable pattern quickly, and once one working request is found, the same technique can be replayed across many hosts. A useful comparison point is the broader web-attack pattern catalogue in the Web Application Attacks Guide, especially the directory traversal and local file inclusion family.
Public exploitation signals matter here because they tell you that patching is no longer just preventative hygiene. They indicate a live attack surface where exposed servers may already have been targeted, scanned, or partially compromised.
What to Check Before You Assume You Are Safe
Start with inventory. Confirm which Apache HTTP Server instances are internet-facing, which ones serve sensitive content, and which ones use Alias-like directives or CGI features that turn a traversal bug into something worse.
Then validate configuration, not just version. A system can be vulnerable in practice because of how it is deployed, even if the application layer seems ordinary. Search web logs, WAF telemetry, reverse proxy logs, and endpoint traces for unusual path encodings, traversal attempts, or unexpected execution of web-facing scripts.
If you need a structured way to prioritise exposure, use the NIST National Vulnerability Database for record-level vulnerability context, the CISA Known Exploited Vulnerabilities Catalog for active exploitation status, and the CVE Program for canonical vulnerability identification.
Risk and Threat Considerations
This CVE matters because confirmed exploitation changes the response from routine vulnerability management to exposure control. If the affected server is reachable and misconfigured, attackers can move from reconnaissance to file access or code execution with very little friction.
Failure mechanism: Requests are crafted to traverse out of intended directories, and in unsafe configurations the server may disclose files or execute content that should have remained inaccessible. That makes the flaw especially dangerous on systems that expose CGI or rely on permissive document mapping.
Impact: The likely outcomes include information disclosure, remote code execution, webshell placement, and downstream compromise of the host or adjacent systems. Because CISA classifies it as actively exploited and links it to ransomware use, defenders should treat exposure as a material incident-prevention problem, not a low-priority patch item.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
MITRE ATT&CK addresses the attack and risk surface, while NIST CSF 2.0, NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST CSF 2.0 | DE.CM-01 — Networks and systems are monitored to detect potential cybersecurity events | Active exploitation requires continuous detection of probing and abnormal web-server activity. |
| Recommendation — Monitor Apache-facing traffic for traversal patterns and suspicious command execution. | ||
| NIST SP 800-53 Rev 5 | SI-2 — Flaw Remediation | The subject is an exploited software flaw that must be remediated quickly. |
| SI-4 — System Monitoring | Confirming exploitation depends on detecting anomalous requests and host behaviour. | |
| Recommendation — Prioritise rapid remediation for the vulnerable Apache deployment. Correlate web, proxy and host telemetry for signs of exploitation. | ||
| CIS Controls v8 | CIS-7 — Continuous Vulnerability Management | KEV-listed flaws require faster prioritisation than ordinary backlog items. |
| Recommendation — Escalate KEV-listed Apache exposure ahead of standard remediation queues. | ||
| MITRE ATT&CK | T1006 — Direct Volume Access | Path traversal abuse is a file-access technique that can support post-exploitation activity. |
| Recommendation — Map suspicious traversal activity to attacker file-access techniques in hunting. | ||
Practitioner Guidance
What to prioritise: First identify every exposed Apache instance, then separate truly vulnerable deployments from systems that are not reachable through the affected paths. If patching is delayed, reduce exposure by removing unnecessary CGI use, tightening path handling, and restricting access to the affected services until the fix is in place.
What to verify: Validate whether the server has already been probed or abused. Look for traversal strings, abnormal request encodings, suspicious child processes spawned by the web server, and any evidence of unexpected file reads or command execution.
Practitioner takeaway: For an exploited CVE, the right question is not only “is it patched?” but “has it already been used against our exposed surface, and what evidence would prove that either way?”
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Reviewed and updated by the NHIMG editorial team on October 19, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org