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changedetection.io project has an XXE vulnerability

High severity GitHub Reviewed Published Apr 27, 2026 in dgtlmoon/changedetection.io • Updated May 4, 2026

Package

pip changedetection.io (pip)

Affected versions

<= 0.54.9

Patched versions

None

Description

changedetection.io_XXE_01 Vulnerability Report: We discovered a XXE vulnerability in the changedetection.io project

While analyzing the code logic, it was determined that an area may lead to unintended behavior under specific conditions. With the project's security in mind, see the analysis results to discern whether this may indicate a potential security risk.

Overview

  • SOURCE_VERSION: 0.54.9 (9f3a9fdc18bba404244801e5df8109e213ce9ff4)
  • Vulnerability type: XXE
  • Finding title: XML XPath helpers parse untrusted XML with entity resolution left to lxml defaults
  • Affected location: changedetectionio/html_tools.py:287

Root Cause

xpath_filter() switches to XML mode for XML/RSS content and creates etree.XMLParser(strip_cdata=False) without explicitly disabling external entity resolution, external DTD loading, or network-backed entity lookup. The helper then parses untrusted XML bytes directly with etree.fromstring(...).

Source-to-Sink Chain

  1. Untrusted XML/RSS response content is fetched from monitored URLs.
  2. Stream detection marks the content as XML/RSS and the include-filter path invokes xpath_filter(..., is_xml=True).
  3. xpath_filter() builds the default XML parser and calls etree.fromstring(...) at changedetectionio/html_tools.py:287.
  4. External entity declarations in attacker XML can be expanded by parser-default behavior in affected runtime combinations.

Exploitation Preconditions

  1. Attacker controls the watched XML/RSS response body.
  2. The watch uses an XPath include filter that triggers XML helper parsing.
  3. Runtime parser behavior allows external entity expansion (for example, vulnerable dependency/default combinations).
  4. The process can read the referenced local resource.

Risk

The XML helper path can turn watch processing into a local file disclosure primitive when entity expansion is enabled by parser defaults.

Impact

Sensitive local files can be exposed into extracted watch output, diff history, and downstream notification channels.

Remediation

  1. Harden XML parser construction with resolve_entities=False, load_dtd=False, and no_network=True.
  2. Reject DOCTYPE/entity declarations for untrusted XML if DTD features are unnecessary.
  3. Add regression tests that assert external entities are never expanded in XPath XML helper flows.

References

@dgtlmoon dgtlmoon published to dgtlmoon/changedetection.io Apr 27, 2026
Published to the GitHub Advisory Database May 4, 2026
Reviewed May 4, 2026
Last updated May 4, 2026

Severity

High

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 Network
Attack Complexity High
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

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:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Improper Restriction of XML External Entity Reference

The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. Learn more on MITRE.

CVE ID

CVE-2026-41895

GHSA ID

GHSA-v7cp-2cx9-x793

Source code

Credits

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