In plain words
Imagine you have a door that can be locked and unlocked with a key, but sometimes the lock gets stuck and can be opened even without the key. This bug is similar, where a part of the web server called mod_rewrite can get stuck and allow hackers to crash the server.
What's broken
The bug is in the mod_rewrite part of the Apache HTTP Server, which is a module that helps with rewriting URLs. It is affected by a use-after-free vulnerability¹ when using a specific feature called lookahead (%{LA-U:HTTP:...}). This means that an attacker could potentially crash the server or do other harmful things. The affected versions are Apache HTTP Server 2.4.0 through 2.4.68.
How it actually works
Here's how it works: when the mod_rewrite module uses the lookahead feature, it can sometimes try to use memory that has already been freed, which is like trying to use a key that has already been thrown away. This can cause the server to crash or behave unexpectedly. The use-after-free vulnerability¹ is a type of bug where the program tries to use something that is no longer available.
Proof of concept
A proof-of-concept² (PoC) is a demonstration that shows the bug really works. In this case, it is not clear from the source if a public PoC exists. If a PoC were available, it would show that the flaw is real and can be reached by an attacker, not just theoretical.
Is it real
It is not clear from the source if this bug is being actively exploited in the wild. The severity of the bug is listed as low.
What to do
To fix this bug, users can update their Apache HTTP Server to a version that is not affected by this vulnerability.
Terms
- ¹ use-after-free vulnerability
- , A type of bug where the program tries to use something that is no longer available.
- ² proof-of-concept
- , A demonstration that shows a bug really works, proving that the flaw is real and can be reached by an attacker.