CVE-2026-54055: Kitty Terminal File Transmission TOCTOU Privilege Escalation

Technical summary

CVE-2026-54055 stems from a TOCTOU (Time-of-Check-Time-of-Use) race condition in Kitty's file transmission protocol implementation. The vulnerable code performs a stat() check on a target file path to validate it, but does not use the O_NOFOLLOW flag when subsequently calling os.open() to create the file. Between the validation check and the file creation, an attacker can replace a normal file with a symlink pointing to a sensitive system path or user file. When the subsequent open() call executes without O_NOFOLLOW, it follows the symlink, allowing writes to unintended locations. The vulnerability requires the attacker to have a child process running within the terminal session and depends on race condition timing. CWE-367 (TOCTOU), CWE-426 (Untrusted Search Path), and CWE-59 (Improper Link Resolution) are all contributing factors.

Business impact

The risk is primarily localized to individual systems where Kitty is actively used. A compromised or malicious child process (such as a script or application launched from the terminal) could overwrite configuration files, application binaries, or user data, potentially leading to privilege escalation within that user's context or system-wide damage if the process has elevated privileges. For organizations standardizing on Kitty for developer workstations or data center terminal access, unpatched instances represent a vector for lateral movement or persistence if an attacker gains initial shell access. The attack requires user interaction and local presence, limiting exploitation scope in most enterprise environments.

Affected systems

Kitty versions prior to 0.47.2 are vulnerable across all supported platforms (Linux, macOS, Windows). The vulnerability manifests in the file transmission protocol, so it affects any Kitty deployment that uses that feature. End users, development teams, and system administrators relying on Kitty for terminal access should verify their installed version and upgrade promptly. Organizations with centralized terminal solutions or bastion hosts running Kitty may face higher risk if those systems are accessed by untrusted users.

Exploitability

Exploitation requires local system access, active user session within Kitty, and the ability to execute code as the authenticated user. The attacker must trigger the file transmission protocol and execute the race condition within a narrow time window—this is technically feasible but not trivial. The CVSS score of 5.0 (Medium) reflects the high bar for triggering the vulnerability: local access, high complexity (AC:H due to race condition timing), low privileges required, and user interaction needed. No public exploit code is known to be in active circulation, and exploitation has not been added to the CISA Known Exploited Vulnerabilities (KEV) catalog.

Remediation

The fix is available in Kitty version 0.47.2, which adds the O_NOFOLLOW flag to the os.open() call, preventing symlink traversal during file creation. All users of earlier versions should upgrade immediately. For organizations unable to patch immediately, consider restricting Kitty's use to trusted environments, disabling the file transmission protocol if possible, or monitoring for suspicious symlink activity in directories where Kitty writes files.

Patch guidance

Upgrade Kitty to version 0.47.2 or later. On Linux distributions using package managers (apt, rpm, etc.), update via your standard patching workflow. macOS users should update via Homebrew or direct download from the official Kitty repository. Windows users should download the latest installer from the Kitty project. Verify the version after patching by running `kitty --version`. Organizations with pinned Kitty versions should schedule updates within their normal maintenance windows, prioritizing systems in sensitive environments (development infrastructure, shared bastion hosts).

Detection guidance

Monitor for failed file creation attempts followed by successful writes to unexpected locations, particularly in system directories or user home directories. Look for symlinks being created in temporary directories or in paths where Kitty's file transmission protocol typically operates. On systems using auditd or similar logging, inspect logs for stat() calls followed shortly by open() calls targeting different paths than the stat() validation. Check Kitty process logs for errors related to file transmission. Intrusion detection systems should flag unusual file creation patterns within terminal sessions, especially repeated race condition attempts.

Why prioritize this

This vulnerability merits timely attention but is not critical. The Medium CVSS score reflects the realistic difficulty of exploitation: race conditions are notoriously finicky, and the attacker must have local access and an active terminal session. However, for organizations where Kitty is widely deployed (especially among developers with access to sensitive systems), the ease of patching and the potential for privilege escalation within a user session justify prioritizing this update over lower-impact flaws. The lack of KEV status indicates real-world exploitation has not been documented at scale. Prioritize patching in multi-tenant environments, CI/CD infrastructure, and bastion hosts; single-developer machines can be addressed in the next regular update cycle if immediate patching poses operational risk.

Risk score, explained

CVSS 5.0 (Medium) is appropriate here. The attack vector is local-only (AV:L), reducing scope significantly compared to network vulnerabilities. Attack complexity is high (AC:H) because the race condition must be precisely timed. Privileges are low (PR:L), meaning any authenticated user can attempt exploitation. User interaction is required (UI:R), adding another barrier. The impact is integrity-focused (I:H) with some availability risk (A:L), but confidentiality is not affected (C:N). Together, these factors yield a moderate risk profile: real but not catastrophic, and entirely mitigable through patching.

Frequently asked questions