CVE-2024-47252

What it actually does

Insufficient escaping of user-supplied SSL/TLS variables (such as SSL_TLS_SNI) in mod_ssl allows an untrusted client to inject arbitrary escape sequences into log files when CustomLog directives reference those variables via %{varname}x or %{varname}c.

Why it matters to the business

Attackers can corrupt or manipulate web-server log files, complicating incident response, enabling log-injection attacks, and potentially masking malicious activity; organizations running affected Apache versions should prioritize patching given the public disclosure and modest but rising exploitability trend.

How an attack unfolds

An attacker initiates an SSL/TLS handshake to a vulnerable Apache instance and supplies a malicious Server Name Indication (SNI) value or other mod_ssl variable containing unescaped control characters; when the server logs the connection using a CustomLog directive that references the variable, the injected characters are written verbatim into the log file, allowing subsequent log tampering or injection.

How to fix it

Upgrade Apache HTTP Server to a fixed release; for the GIT tree apply commit 7e926454793abd7d71b6afc8bd1ec1648752c6ad, and for Debian 13 install version 6.12.35-1 or later. Review CustomLog configurations that reference mod_ssl variables and consider removing or sanitizing those references until patches are applied.

How to confirm the fix worked

Confirm the running Apache binary reports a version newer than 2.4.63 or contains the cited commit; test by sending an SNI containing control characters and verifying that the resulting log line no longer contains raw escape sequences.

Typical attack path

1. Identify a target Apache HTTP Server exposing HTTPS.
2. Craft an SSL/TLS ClientHello containing a malicious SNI or other mod_ssl variable with escape characters.
3. Complete the handshake to trigger logging of the supplied variable.
4. Inspect or further manipulate the resulting log entries to achieve log injection or evasion.

How to detect it

Review web-server access and error logs for entries containing unexpected control characters or escape sequences in fields normally populated by mod_ssl variables such as SSL_TLS_SNI; correlate with TLS handshake metadata to identify client-supplied values that appear unescaped.

What your security team should do

• Apply the listed fixed versions immediately on all internet-facing Apache instances.
• Audit CustomLog directives for references to mod_ssl variables and remove or sanitize them where possible.
• Monitor EPSS trend and re-evaluate exploit maturity; prepare to accelerate remediation if exploitation is observed in the wild.