CVE-2025-65082 is a fresh vulnerability discovered in the Apache HTTP Server, affecting all versions from 2.4. through 2.4.65. This bug revolves around the improper neutralization of escape, meta, or control sequences within environment variables—specifically, when these are set via the Apache configuration and not sanitized as strictly as required. If you’re running CGI scripts behind Apache, this one is important for you!
What’s the Issue?
When you configure Apache’s SetEnv or similar directives, you can push custom environment variables into the runtime of CGI programs. Normally, some environment variables are generated by the Apache server itself for CGI use (REMOTE_ADDR, QUERY_STRING, etc.).
The vulnerability happens when an attacker can manipulate an environment variable you’ve “pre-set” in the Apache configuration (think: SetEnv QUERY_STRING evil-content). These pre-set variables win over Apache’s secure, internally generated ones and land directly in your CGI app—potentially including unsafe escape, meta, or control sequences.
By leveraging this behavior, an attacker may inject untrusted input or even control CGI execution paths, leading to request manipulation, information disclosure, or even, under specific conditions, code execution.
Let’s say your Apache config (httpd.conf or .htaccess) includes
SetEnv QUERY_STRING "anything"
Your CGI script expects QUERY_STRING to reflect the value from the incoming HTTP request, but now it always gets anything, because your setting overrides the secure value.
Worse, if an attacker has any influence over these pre-set strings, or if you set them using unsanitized user input, control or escape sequences can be injected directly.
Imagine the setting
SetEnv QUERY_STRING ";cat /etc/passwd;"
A poorly-written CGI script invoking shell commands using QUERY_STRING could actually run system-level commands. Here’s a simple Perl CGI example showing the danger:
#!/usr/bin/perl
print "Content-type: text/html\n\n";
my $query = $ENV{'QUERY_STRING'};
system("echo $query"); # Untrusted!
With the bad SetEnv, the above will execute cat /etc/passwd as the Apache user.
Note: The risk is compounded if scripts “trust” environment variables provided by Apache, which is a common (if flawed) practice.
Technical Details
Affected: Apache HTTP Server 2.4. – 2.4.65
Patched In: 2.4.66
Vulnerable Configuration
- Any direct SetEnv (or PassEnv, UnsetEnv, etc.) of variables also set by Apache internally for CGI
No neutralization or sanitization of values
Original Apache Documentation on CGI Environment Variables
Security Advisory Reference (CVE-2025-65082)
How to Check for Vulnerability
- Look for SetEnv lines in your config that set variables like QUERY_STRING, REMOTE_ADDR, etc.
To check programmatically (in Linux)
grep SetEnv /etc/httpd/conf*/*.conf | grep -E 'QUERY_STRING|HTTP_|REMOTE_'
How to Fix
1. Upgrade!
Patch to Apache HTTP Server 2.4.66 (download from the official source). This version neutralizes or ignores problematic overrides.
2. Audit Configs
Remove or revise SetEnv lines setting standard CGI variables.
3. Don’t Use User Input in Env Vars
Sanitize or reject input if you must use it.
References & Links
- CVE Record for CVE-2025-65082
- Apache HTTP Server Security Page
- Apache CGI Environment Variable Docs
- How To Configure SetEnv and UnsetEnv
Final Notes
This bug highlights the dangers of blindly mixing configuration-time and runtime data, especially in legacy tech stacks like CGI. Apache’s patch ensures its own computed variables aren’t overwritten so easily in the future. Until you’ve upgraded to 2.4.66, make sure you’re not overriding critical CGI environment variables—especially with anything user-controlled!
For best security, always sanitize any data passed to CGI scripts, and keep your software up to date.
Timeline
Published on: 12/05/2025 10:46:27 UTC
Last modified on: 12/10/2025 16:39:56 UTC