CVE-2017-9798

What it actually does

Use-after-free vulnerability in Apache HTTP Server allows unauthenticated remote attackers to read arbitrary process memory contents via specially crafted OPTIONS requests when the Limit directive is configurable via .htaccess or httpd.conf misconfigurations.

Why it matters to the business

Potential exposure of sensitive data such as authentication credentials or internal configuration from server memory increases risk of credential theft and downstream breaches; high EPSS indicates strong exploit likelihood despite absence from KEV.

How an attack unfolds

An attacker sends an unauthenticated OPTIONS HTTP request to a vulnerable Apache instance where Limit sections can be influenced; the use-after-free condition causes freed memory containing secrets to be returned in the response, though success varies due to memory layout and configuration factors.

How to fix it

Upgrade Apache HTTP Server to versions beyond 2.2.34 and 2.4.27; apply the referenced patch to ap_limit_section in server/core.c if immediate upgrade is not feasible; restrict .htaccess capabilities for Limit directives.

How to confirm the fix worked

Confirm Apache version is newer than 2.2.34/2.4.27, test OPTIONS requests against Limit-protected resources to verify no memory disclosure occurs, and review server/core.c for the applied fix.

Typical attack path

1. Identify target Apache HTTP Server instances via banner or behavior analysis
2. Confirm presence of .htaccess support or Limit directive exposure
3. Craft and send OPTIONS request targeting Limit section handling
4. Parse response for leaked process memory contents containing secrets
5. Leverage obtained data for further authentication or lateral movement

How to detect it

Review web server access logs for anomalous OPTIONS requests; inspect responses for non-standard content lengths or unexpected data patterns; check for use of .htaccess files containing Limit sections.

What your security team should do

• Prioritize upgrade of all Apache HTTP Server instances to patched releases given weaponized exploit maturity and stable high EPSS
• Audit .htaccess and httpd.conf configurations to disable or restrict Limit directive usage where possible
• Monitor for OPTIONS requests returning unusually large or variable responses as potential exploitation indicators