vim: vim use after free (CVE-2025-26603) #shorts

Summary

Today, we are diving into a recent critical vulnerability, CVE-2025-26603, which impacts Vim, a popular UNIX text editor. This vulnerability could potentially allow attackers to exploit a use-after-free condition, leading to a buffer overflow.

Product details

Vim, which stands for 'Vi IMproved', is an enhanced version of the UNIX editor Vi. It's widely used for programming because of its powerful functionalities for source code editing.

Vulnerability type summary

The vulnerability associated with CVE-2025-26603 is identified as CWE-416: Use After Free. This occurs when a program frees a resource and then inadvertently tries to use that resource again, potentially leading to unpredictable behavior or a security breach.

Details of the vulnerability

In CVE-2025-26603, the problem arises from Vim's ability to redirect screen messages using the `:redir` command. The issue occurs within the ex_display() function, where Vim may attempt to access memory related to registers that have already been freed, specifically affecting operations connected to the clipboard registers `*` and `+`. The vulnerability exists in Vim versions below 9.1.1115. Fedora has issued security updates for Vim to mitigate this vulnerability in versions 40 and 41.

Conclusion

CVE-2025-26603 is a critical vulnerability that requires immediate attention from Vim users. Users running affected versions should upgrade to the latest patched version, 9.1.1115, to protect their systems from potential exploitation. Stay vigilant and ensure your software is always up to date to mitigate such risks.

Watch the full video on YouTube: CVE-2025-26603

Remediation and exploitation details

This chain involves the following actors

This following systems are involved

Attack entry point

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CVE database technical details

CVE ID

CVE-2025-26603

Description

Vim is a greatly improved version of the good old UNIX editor Vi. Vim allows to redirect screen messages using the `:redir` ex command to register, variables and files. It also allows to show the contents of registers using the `:registers` or `:display` ex command. When redirecting the output of `:display` to a register, Vim will free the register content before storing the new content in the register. Now when redirecting the `:display` command to a register that is being displayed, Vim will free the content while shortly afterwards trying to access it, which leads to a use-after-free. Vim pre 9.1.1115 checks in the ex_display() function, that it does not try to redirect to a register while displaying this register at the same time. However this check is not complete, and so Vim does not check the `+` and `*` registers (which typically donate the X11/clipboard registers, and when a clipboard connection is not possible will fall back to use register 0 instead. In Patch 9.1.1115 Vim will therefore skip outputting to register zero when trying to redirect to the clipboard registers `*` or `+`. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Provider

GitHub_M

CWE / problem types

CWE-416: Use After Free

Affected Software Versions

vim:vim:[{'version': '< 9.1.1115', 'status': 'affected'}]

Date Published

2025-02-18T19:04:24.273Z

Last Updated

2025-03-07T00:10:51.265Z