On Windows in versions of grep-cli prior to 0.1.6, it's possible for some of the routines to execute arbitrary executables. In particular, a quirk of the Windows process execution API is that it will automatically consider the current directory before other directories when resolving relative binary names. Therefore, if you use grep-cli to read decompressed files in an untrusted directory with that directory as the CWD, a malicious actor to could put, e.g., a gz.exe binary in that directory and grep-cli will use the malicious actor's version of gz.exe instead of the system's.

This is also technically possible on Unix as well, but only if the PATH variable contains .. Conventionally, they do not.

A DecompressionReader has been fixed to automatically resolve binary names using PATH, instead of relying on the Windows API to do it.

If you use grep-cli's CommandReader with a std::process::Command value on Windows, then it is recommended to either construct the Command with an absolute binary name, or use grep-cli's new resolve_binary helper function.

To be clear, grep-cli 0.1.6 mitigates this issue in two ways:

• A DecompressionReader will resolve decompression programs to absolute paths automatically using the PATH environment variable, instead of relying on Windows APIs to do it (which would result in the undesirable behavior of checking the CWD for a program first).
• A new function, resolve_binary, was added to help users of this crate mitigate this behavior when they need to create their own std::process::Command. For example, ripgrep uses grep_cli::resolve_binary on the argument given to its --pre flag.

While the first mitigation fixes this issue for sensible values of PATH when doing decompression search, the second mitigation is imperfect. The more fundamental issue is that std::process::Command is itself vulnerable to this.

The Rust Security Response WG was notified that the regex crate did not properly limit the complexity of the regular expressions (regex) it parses. An attacker could use this security issue to perform a denial of service, by sending a specially crafted regex to a service accepting untrusted regexes. No known vulnerability is present when parsing untrusted input with trusted regexes.

This issue has been assigned CVE-2022-24713. The severity of this vulnerability is "high" when the regex crate is used to parse untrusted regexes. Other uses of the regex crate are not affected by this vulnerability.

Overview

The regex crate features built-in mitigations to prevent denial of service attacks caused by untrusted regexes, or untrusted input matched by trusted regexes. Those (tunable) mitigations already provide sane defaults to prevent attacks. This guarantee is documented and it's considered part of the crate's API.

Unfortunately a bug was discovered in the mitigations designed to prevent untrusted regexes to take an arbitrary amount of time during parsing, and it's possible to craft regexes that bypass such mitigations. This makes it possible to perform denial of service attacks by sending specially crafted regexes to services accepting user-controlled, untrusted regexes.

Affected versions

All versions of the regex crate before or equal to 1.5.4 are affected by this issue. The fix is include starting from regex 1.5.5.

Mitigations

We recommend everyone accepting user-controlled regexes to upgrade immediately to the latest version of the regex crate.

Unfortunately there is no fixed set of problematic regexes, as there are practically infinite regexes that could be crafted to exploit this vulnerability. Because of this, we do not recommend denying known problematic regexes.

Acknowledgements

We want to thank Addison Crump for responsibly disclosing this to us according to the Rust security policy, and for helping review the fix.

We also want to thank Andrew Gallant for developing the fix, and Pietro Albini for coordinating the disclosure and writing this advisory.