The Common Vulnerabilities and Exposures (CVE) system has recently assigned the identifier CVE-2023-29132 to a specific use-after-free vulnerability discovered in the widely utilized IRC client, Irssi. Versions 1.3.x and 1.4.x prior to version 1.4.4 suffer from this vulnerability, which occurs due to a stale special collector reference being used when printing a non-formatted line concurrently with a formatted one. This post will delve into the details of this vulnerability, provide code snippets to understand the issue better, and offer links to relevant references.

The Vulnerability: Use-After-Free

Irssi, as an IRC client, allows users to connect to various IRC networks and chat servers to engage in real-time, text-based conversations. In doing so, proper handling of printed text on the user's end is essential for efficient communication. The use-after-free vulnerability discovered in Irssi revolves around the mishandling of printed text under certain circumstances.

In programming, a use-after-free vulnerability is created when a program continues to use a memory location after it has been freed, which can result in undefined behavior, crashes, or even the execution of arbitrary code by an attacker. In this case, Irssi faces a significant vulnerability that revolves around the simultaneous printing of formatted and non-formatted lines of text.

Code Snippet: The Issue

To understand the use-after-free vulnerability better, let's take a look at the offending code in question:

static void sig_print_text_plain(TEXT_DEST_REC *dest, const char *text,
                                 int formatnum, TEXT_CHUNK_REC *lastchunk)
  last_chunk = create_chunk(dest, last_chunk);

The problem is the assignment of the last_chunk variable when printing a non-formatted line. Since last_chunk is not properly updated during the printing process and is reused within the sig_print_text_plain function, a stale special collector reference is used inadvertently.

Exploit Details

An attacker could potentially exploit this vulnerability by sending specifically crafted messages to a victim, causing undefined behavior or crashes in the Irssi application. Although the likelihood of a successful attack depends on various factors, including the victim's configuration and the attacker's knowledge of the target, it is crucial for users to update to the latest version to mitigate this risk.

Original References

The vulnerability was discovered and documented in the Irssi development community, and it is recommended to consult original references for a more in-depth understanding:

1. Irssi Security Advisory:
2. ChangeLog outlining the fixes:
3. Commit fixing the vulnerability on GitHub:


CVE-2023-29132 highlights a significant use-after-free vulnerability in Irssi versions 1.3.x and 1.4.x before 1.4.4, which revolves around the improper handling of printed text during concurrent printing. To secure their systems and ensure efficient communication, users must upgrade to the latest version of Irssi, which addresses this vulnerability. Additionally, it is essential for the development community to stay vigilant, addressing vulnerabilities promptly to uphold the security and integrity of the software ecosystem.


Published on: 04/14/2023 01:15:00 UTC
Last modified on: 04/24/2023 13:24:00 UTC