In recent years, Windows terminal emulators have become essential tools. ConEmu is one of the most popular ones, but sometimes even trusted apps have critical flaws. In this long read, we break down CVE-2023-39150, a bug that could let an attacker execute code on your system by messing with window title responses in ConEmu. We’ll cover the technical details, show code examples, explain the exploit, and point you toward further references.

What is CVE-2023-39150?

CVE-2023-39150 is a security vulnerability found in ConEmu, a powerful Windows console emulator. The issue was discovered before commit 230724, where the program failed to properly sanitize title responses that included control characters.

This vulnerability is especially worrisome because it opens the door to arbitrary code execution—in other words, someone could run malicious code on your computer just by sending a tricky window title update! This flaw is related to an incomplete fix for CVE-2022-46387.

Understanding the Flaw

ConEmu, like many terminal emulators, supports updating its window title by interpreting special escape sequences. These typically look like this:

echo -e "\033];New Title\007"

\007 : Ends the command with a bell character.

However, in affected versions, ConEmu didn’t properly filter out all control characters—special non-printable characters—when it received title commands in response. This is dangerous because embedded scripts or special characters within the title can be interpreted in unintended ways, leading to exploit possibilities.

Let’s see how an attacker could exploit this.

Suppose an attacker controls a remote system you are SSH’ing into or sends you a crafted file. The attacker can use a control character in the window title sequence as follows:

echo -e "\033];malicious_title\033[1;31m\007"

Here, \033[1;31m is an ANSI escape sequence to switch text to red, but more advanced obfuscation or terminal escape codes could be used. An attacker can go further and try to inject sequences that trigger functions or even execute code through buggy parsing, depending on how the host (ConEmu) handles such input.

Exploit Example

Let’s say we have a ConEmu terminal connected to a malicious server (via SSH or similar). The server could send back a response like this:

echo -e "\033];$(calc.exe)\007"

In vulnerable ConEmu versions, the shell substitution $(calc.exe) is not directly executed because ConEmu doesn't parse bash commands. But suppose a more complex example where a parser bug could actually pass this into an evaluated context. In the real world, attackers often chain vulnerabilities together. At the very least, escape codes can break the terminal interface, steal information or trick users.

More likely, the attacker’s payload will include crafted control characters to break out of the title context and inject further sequences:

malicious_title = '\033];Compromised Title\033`;malicious_command\007'
print(malicious_title)

With an unpatched ConEmu, such sequences could interact with the system in unexpected ways. For example, a link click or copy-paste might trigger a malicious action injected this way.

Timeline: How the Bug Was Fixed

After CVE-2022-46387 was not properly closed, the issue was reported and tracked as CVE-2023-39150. The fix is available in commit 230724, where the developers added stronger sanitization of control characters in title responses.

How to Stay Safe

1. Update ConEmu: Always run the latest version. Get it here.

Be careful with untrusted sources: Don’t connect your terminal to hosts you don’t trust.

3. Monitor CVE disclosures: Use resources like NVD and GitHub.
4. Disable risky terminal features: In settings, limit terminal interpretation if you’re working in high-risk environments.

References & Further Reading

- Official CVE-2023-39150 page
- ConEmu GitHub fix
- CVE-2022-46387: Previous incomplete fix
- Original issue discussion
- Escape Sequence Documentation

Conclusion

CVE-2023-39150 is a textbook reminder: never trust input, especially in complex, multi-layered applications like terminal emulators. Even a small window title can be a security risk! If you use ConEmu, make sure you’re patched, and keep an eye on future CVEs.

Stay safe, and patch your software!

*This post is exclusive and written in clear, simple American English. All code and exploit details are for educational awareness only.*

Timeline

Published on: 09/12/2023 13:15:07 UTC
Last modified on: 10/05/2023 13:14:16 UTC