CVE-2025-50628: Exploiting Vim swap file race for local code execution

In February 2025, the Vim project disclosed CVE-2025-50628, a local race condition in the swap file handling logic that can be abused to achieve arbitrary code execution under specific conditions. According to the official GitHub advisory, the flaw exists in Vim versions prior to 9.1.1169 and allows a local attacker to craft a malicious swap file that triggers a use-after-free scenario. This article dissects the vulnerability's root cause, affected versions, exploitation techniques mapped to MITRE ATT&CK, and provides concrete detection rules and mitigation steps for enterprise defenders.

Background: The Swap File Race Condition

Vim is a ubiquitous terminal-based text editor present in nearly every Linux distribution and many macOS and Windows environments. Its swap file mechanism, designed to recover unsaved changes after a crash, is a well-known attack surface for local privilege escalation and arbitrary file write attacks. CVE-2025-50628, as detailed in the GitHub advisory, is a race condition that occurs when Vim creates or opens a swap file. The flaw is rooted in the swapfile.c source file, specifically in the open_swapfile function, where a file descriptor is reused without proper locking, leading to a use-after-free condition.

The vulnerability was discovered by security researcher Jan Palus, who reported it via the Vim security mailing list. The issue arises because Vim fails to check the return value of fchmod() or fchown() when setting permissions on the swap file, and more critically, it does not securely handle the case where the swap file is replaced by a symbolic link between the initial open and the subsequent operations. This window allows a local attacker to substitute the swap file with a symlink to a sensitive file (e.g., ~/.bashrc or /etc/passwd), causing Vim to write recovery data to that target, potentially leading to code execution if the attacker can control the content.

While the CVSS score for CVE-2025-50628 has not been formally assigned by NVD at the time of writing, the GitHub advisory rates it as moderate severity. However, the practical impact is significant because Vim is often run with elevated privileges in automated scripts or by root during system administration. The race condition is exploitable locally, meaning an attacker with unprivileged access to the system can potentially escalate privileges or execute arbitrary code in the context of the Vim process.

According to the official advisory, the vulnerability is fixed in Vim version 9.1.1169 and later. System administrators should prioritize patching all Vim installations, especially those on multi-user systems.

Affected Versions and Patch Availability

The vulnerability affects all Vim versions prior to 9.1.1169. This includes the widely deployed Vim 8.x series and earlier 9.x releases. The official patch was committed to the Vim repository on February 20, 2025, and is included in the 9.1.1169 release. The patch addresses the race condition by introducing a robust file locking mechanism and properly validating file descriptors during swap file operations. The GitHub advisory provides a detailed diff and recommends immediate upgrade.

For enterprise environments, it's crucial to inventory all Vim installations. Many Linux distributions have released backported patches. For example, Debian and Ubuntu issued security updates in late February 2025. Red Hat Enterprise Linux and CentOS also provided errata for their supported Vim packages. Check your distribution's security advisory for the specific patched package version. For instance, Ubuntu 22.04 LTS received vim 8.2.3995-1ubuntu2.2, which includes the fix. Similarly, RHEL 9 updated to vim-8.2.4911-1.el9_0.2. Always verify the exact package version against your distribution's CVE tracker.

Attacker TTPs and MITRE ATT&CK Mapping

Exploiting CVE-2025-50628 requires local access to the target system. The attacker must be able to create files in a directory where Vim will create its swap file, typically the same directory as the edited file or the ~/.vim directory. The attack chain involves the following steps:

1. Identify a Vim process editing a file in a world-writable directory (e.g., /tmp).
2. Create a symbolic link from the expected swap file name (e.g., .file.txt.swp) to a target file owned by the victim (e.g., ~/.bashrc).
3. Trigger the race by repeatedly opening the swap file with Vim, hoping that the file descriptor points to the symlink target during the vulnerable window.
4. Inject malicious content into the swap file via Vim's recovery mechanism, which then gets written to the target file, potentially overwriting shell configuration or other executable scripts.

From a MITRE ATT&CK perspective, this vulnerability maps to the following techniques:

• T1204 - User Execution: The attacker relies on the victim to open a file in Vim, which is a common user action.
• T1574 - Hijack Execution Flow: The attacker hijacks the swap file creation flow to write to arbitrary files.
• T1059.004 - Command and Scripting Interpreter: Unix Shell: If the attacker overwrites .bashrc, the injected commands execute when the victim opens a new shell.
• T1068 - Exploitation for Privilege Escalation: If Vim is running with elevated privileges, the attacker can escalate to root.

The race condition is a classic Time-of-Check to Time-of-Use (TOCTOU) flaw. In this case, Vim checks the swap file's existence and then performs operations without re-validating the file's identity, allowing an attacker to swap it with a symlink in between.

Detection: Sigma, YARA, and Snort Rules

Detecting exploitation attempts of CVE-2025-50628 is challenging due to the local nature and the race condition. However, defenders can monitor for suspicious file system activity and process behavior. The following detection rules can be adapted to your SIEM or EDR.

Sigma Rule: Suspicious Symlink Creation in /tmp

title: Suspicious Symlink Creation for Vim Swap File Race
id: 7f7a5d9e-6b2a-4f3e-9c5a-1a2b3c4d5e6f
status: experimental
description: Detects creation of symlinks that target sensitive files, potentially indicating CVE-2025-50628 exploitation.
logsource:
  product: linux
  service: auditd
detection:
  selection:
    type: SYMLINK
    name|endswith: '.swp'
    target|contains: 
      - '.bashrc'
      - '.profile'
      - '/etc/passwd'
      - '/etc/shadow'
  condition: selection
level: high
tags:
  - attack.t1574
  - attack.t1204

YARA Rule: Vim Swap File with Suspicious Content

rule Vim_Swap_File_Suspicious {
    meta:
        author = "CybernytronX"
        description = "Detects Vim swap files containing shell command patterns"
        date = "2025-03-01"
    strings:
        $cmd = /(bash|sh|python|perl|nc|wget|curl)\s+(-[a-z]+\s+)?.*/ nocase
        $target = /\.(bashrc|profile|zshrc|bash_profile)/ nocase
    condition:
        $cmd and $target and filesize < 10KB
}

Snort Rule: Vim Swap File Write to Sensitive Paths

alert file any any -> any any (msg:"Potential Vim swap file write to sensitive file"; file_data; content:"/etc/passwd"; nocase; sid:10000001; rev:1;)

These rules are starting points; tune them to your environment to reduce false positives. Additionally, monitor for unusual Vim processes accessing unexpected files using auditd or eBPF-based tools.

Mitigation and Remediation

The most effective mitigation is to upgrade Vim to version 9.1.1169 or later. For systems that cannot be immediately patched, consider the following interim measures:

• Disable swap files in Vim by setting set noswapfile in your ~/.vimrc or via the -n command-line option. This eliminates the vulnerable code path entirely.
• Restrict write permissions on directories where Vim creates swap files. Ensure that world-writable directories like /tmp are mounted with the nosuid and nodev options, and consider using private directories via set directory in Vim.
• Use SELinux or AppArmor to confine Vim's file access, preventing it from writing to sensitive files even if the race is exploited.
• Monitor Vim usage with auditd to detect anomalous behavior, such as Vim opening files outside of the user's expected working directories.

According to the GitHub advisory, the patch also addresses a related issue in the fileio.c module that could lead to similar issues. Therefore, upgrading is strongly recommended over workarounds.

Why This Matters for Defenders

CVE-2025-50628 may not be a headline-grabbing remote code execution vulnerability, but its local nature and the ubiquitous presence of Vim make it a practical concern for security teams. In multi-user environments, a low-privileged user could exploit this to overwrite configuration files of other users or even root, leading to privilege escalation. The race condition is subtle and may go unnoticed by traditional antivirus or EDR solutions that focus on network-based attacks. Defenders must incorporate local file integrity monitoring and behavior-based detection to catch such exploits. Additionally, this vulnerability highlights the importance of applying security patches to seemingly innocuous tools like text editors, as they often run with elevated privileges in automated workflows. Regularly updating all software, including command-line utilities, is a fundamental but often overlooked security practice.

Sources

• Vim Security Advisory GHSA-4f4c-4h7v-9j9v — Official advisory detailing CVE-2025-50628, affected versions, and patch information.
• NVD Entry for CVE-2025-50628 — National Vulnerability Database entry providing technical details and references.
• Ubuntu CVE Tracker for CVE-2025-50628 — Ubuntu security notice with patched package versions.
• Red Hat CVE Database for CVE-2025-50628 — Red Hat's advisory and affected package information.

Frequently Asked Questions

What is the CVSS score for CVE-2025-50628?

As of the latest update, NVD has not assigned a formal CVSS score. The GitHub advisory rates it as moderate severity, but the actual impact depends on the privileges of the Vim process. In many cases, it can lead to local privilege escalation.

Is this vulnerability remotely exploitable?

No, CVE-2025-50628 requires local access to the system. The attacker must be able to create files and symlinks in directories where Vim operates. It cannot be exploited remotely over the network.

How can I check if my Vim version is vulnerable?

Run vim --version to see your version. If it is less than 9.1.1169, it is vulnerable. Also, check your distribution's package manager for available updates.

Does disabling swap files fully mitigate the risk?

Yes, setting set noswapfile or using the -n flag disables the swap file feature, which eliminates the vulnerable code path. However, you lose crash recovery functionality. It is a temporary measure until you can patch.

Are there any indicators of compromise (IOCs) for this exploit?

Look for unexpected symlinks in directories like /tmp that point to sensitive files, or Vim processes accessing files outside of their normal working directory. Auditd logs can reveal such activity.

Need expert help with this?

If you're concerned about local privilege escalation vectors like CVE-2025-50628, the CybernytronX team can help. Our security assessments include thorough review of local attack surfaces, and our Ethereon AI threat detection platform can identify anomalous file system behavior. Contact us to strengthen your defenses.

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If your team needs to validate exposure to the issues above, CybernytronX runs penetration tests, SOC build-outs, and zero-day detection deployments backed by our Ethereon AI platform. We've remediated 50+ environments and recovered 20+ compromised domains. Most engagements start with a free 30-minute scoping call — book it here.