CVE-2026-25635
Description
A flaw was found in Calibre's CHM reader. This path traversal vulnerability allows an attacker to write arbitrary files to locations where the user has write permissions. On Windows systems, this could lead to remote code execution by placing a malicious file in the Startup folder, which would then execute upon the user's next login. This vulnerability primarily results in arbitrary code execution.
Statement
This IMPORTANT flaw in Calibre's CHM reader allows an attacker to perform path traversal, leading to arbitrary file writes. This could enable an attacker to write malicious files to arbitrary locations on the filesystem where the user has write permissions. Exploitation requires a user to open a specially crafted CHM file.
Mitigation
Users should avoid opening untrusted CHM files with Calibre. This operational control reduces the risk of exploitation by preventing the processing of malicious content.
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
The attacker may be able to create or overwrite critical files that are used to execute code, such as programs or libraries.
Integrity
Technical Impact: Modify Files or Directories
The attacker may be able to overwrite or create critical files, such as programs, libraries, or important data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, appending a new account at the end of a password file may allow an attacker to bypass authentication.
Confidentiality
Technical Impact: Read Files or Directories
The attacker may be able read the contents of unexpected files and expose sensitive data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, by reading a password file, the attacker could conduct brute force password guessing attacks in order to break into an account on the system.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
The attacker may be able to overwrite, delete, or corrupt unexpected critical files such as programs, libraries, or important data. This may prevent the product from working at all and in the case of protection mechanisms such as authentication, it has the potential to lock out product users.
Frequently Asked Questions
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