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Path Traversal Leading to Arbitrary File Write and Potentially Code Execution

Critical
kovidgoyal published GHSA-72ch-3hqc-pgmp Feb 20, 2026

Package

No package listed

Affected versions

< 9.2.1

Patched versions

9.3.0

Description

Summary

Calibre's ODT reader contains a path traversal vulnerability that allows arbitrary file writes anywhere the user has write permissions. On Windows, this leads to Remote Code Execution by writing a payload to the Startup folder, which executes on next login.

Details

Confirmed on: Calibre 9.2.1, Windows 11 (x64)
Trigger: Converting a malicious ODT file via GUI ("Convert books")

Affected Component: src/calibre/ebooks/odt/input.py

Vulnerable Code (Lines 28-35):

def extract_pictures(self, zf):
    if not os.path.exists('Pictures'):
        os.makedirs('Pictures')
    for name in zf.namelist():                                          # ATTACKER CONTROLLED
        if name.startswith('Pictures') and name not in {'Pictures', 'Pictures/'}:
            data = zf.read(name)
            with open(name, 'wb') as f:                                 # PATH TRAVERSAL
                f.write(data)                                           # ARBITRARY FILE WRITE

Only checks startswith('Pictures'), does not sanitize .. sequences. Calibre's own ZipFile.extractall() in utils/zipfile.py does sanitize .. via _get_targetpath(), but extract_pictures() bypasses this by using manual zf.read() + open().

Attack Flow:

  1. Malicious ODT (which is a ZIP) contains entry: Pictures/../../../../../Roaming/Microsoft/Windows/STARTM~1/Programs/Startup/rce.bat
  2. zf.namelist() returns this name with .. intact
  3. name.startswith('Pictures') passes
  4. open(name, 'wb') resolves .. traversal, writes to Startup folder
  5. Payload executes on next Windows login

PoC:

> python3 create_poc.py
[+] poc.odt

# Convert via GUI "Convert books"

> dir "%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup"
rce.bat

# Reboot → calc.exe launches automatically

Proof Files:

  • create_poc.py — Standalone PoC generator

create_poc.py

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction Active
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality High
Integrity High
Availability High

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

CVE ID

CVE-2026-26064

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

Credits