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Authelia has an Edge Case Access Control Rule Mismatch

Low severity GitHub Reviewed Published May 26, 2026 in authelia/authelia • Updated Jun 26, 2026

Package

gomod github.com/authelia/authelia/v4 (Go)

Affected versions

>= 4.36.0, <= 4.39.19

Patched versions

4.39.20

Description

Impact

CVSSv4 Baseline Score: Low 2.4

CVSSv4 Weighted Score: Low 1.3

The full CVSSv4 Vector for this vulnerability is:

CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N/E:P/CR:H/IR:L/AR:L/MAV:N/MAC:H/MAT:P/MPR:L/MVC:L/MVI:N/MVA:N/MSC:L/MSI:N/MSA:N/S:N/AU:Y/R:U/V:D/RE:L/U:Amber

CVSSv3.1 Baseline Score: Low 3.1

CVSSv3.1 Overall Score: Low 3.4

The full CVSSv3.1 Vector equivalent for this vulnerability is:

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N/E:P/RL:O/RC:C/CR:H/IR:L/AR:L/MAV:N/MAC:H/MPR:L/MUI:X/MS:U/MC:L/MI:N/MA:N

The weighted severity rating is a result of no indication this is currently being exploited being available at the time of the publish date, in addition to the fact it's unlikely that it is being exploited currently. The vectors have been picked based on the scenario most likely to exist in real configurations.

In addition to the weighting our assessment considers the fact the configuration scenario required for this vulnerability to be exploited is highly unlikely and an attacker is unlikely in most scenarios to be able to determine if the exploit is available and if it was successful except in rare situations. Though the visibility to the attacker was not reflected in our assessment.

Summary

Due to lack of canonicalization of domains in very specific edge cases an access control rule may be skipped when it should match a request.

Details

This attack vector must be executed in a highly specific scenario which we do not believe any user would find themselves in. In an abundance of caution we are issuing this advisory and would appreciate any users who find this configuration report it to us with both the access control section, and sessions section so that we can best advise the community of the actual impact.

The specific conditions that could lead to a security issue for vulnerability are as follows:

  1. The specific target resource of the attack must be using the forwarded authorization integration.
  2. The requested domain must have two additional segments compared to a session domain i.e. a.b.example.com is requested, but the session domain is example.com.
  3. There access control rules must specify two separate rules which both contain inexact domain matches such as *.b.example.com and *.example.com i.e. wildcards, username matches, group matches.
  4. The rules must be in order of most specific domain to least specific domain.
  5. The second rule must be more permissive than the first rule.
  6. The second rule must also match all criteria of the given request.
  7. The attacker must specifically request a URL for the more specific domain, with the second part containing one or more capitalized letters i.e. https://a.B.example.com and no other segment with capitalized letters.
  8. The integration used must not be the Envoy ExtAuthz integration.
  9. The proxy must not canonicalize the requested host name in the relevant header before sending it to the relevant authorization endpoint.

The kind of configuration used to produce this issue and result in a bypass rule being matched has long been highly discouraged. Essentially hosts which should be bypassed entirely should not be secured by having the proxy check them with the authorization handlers.

It should also be noted this has been heavily mitigated due to another bug where the session domain would not match if any part of the configured session domain was capitalized (fixed in authelia/authelia@368631e, it should be expressly noted this commit does not contain a fix for a CVE). This bug would prevent the request from succeeding in any way. This bug will also be fixed after this vulnerability is fixed, and the bug where session domains would not match has no security impact other than heavily mitigating the access control vulnerability.

Patches

Upgrade to 4.39.20.

Commit: authelia/authelia@b6d1d60

Workarounds

See the below examples for configurations to avoid.

Examples

1FA Downgrade

The following example could result in a 1FA downgrade.

Request URL: https://a.B.example.com

Configuration:

session:
  cookies:
    - domain: 'example.com'
      authelia_url: 'https://example.com'
access_control:
  rules:
     - domain: '*.b.example.com'
       policy: 'two_factor'
     - domain: '*.example.com'
       policy: 'one_factor'
Bypass Downgrade

The following example could result in a bypass downgrade. It should be noted that configurations like this have long been discouraged. The domains matching the pattern *.example.com should not be configured to forward authorization requests to Authelia in most situations.

Request URL: https://a.B.example.com

Configuration:

session:
  cookies:
    - domain: 'example.com'
      authelia_url: 'https://example.com'
access_control:
  rules:
     - domain: '*.b.example.com'
       policy: 'two_factor'
     - domain: '*.example.com'
       policy: 'bypass'
Unaffected Scenario

The following configuration is unaffected regardless of the request.

session:
  cookies:
    - domain: 'example.com'
      authelia_url: 'https://example.com'
access_control:
  rules:
     - domain: 'b.example.com'
       policy: 'two_factor'
     - domain: '*.example.com'
       policy: 'one_factor'

References

@james-d-elliott james-d-elliott published to authelia/authelia May 26, 2026
Published by the National Vulnerability Database Jun 19, 2026
Published to the GitHub Advisory Database Jun 26, 2026
Reviewed Jun 26, 2026
Last updated Jun 26, 2026

Severity

Low

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 Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality Low
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality Low
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:L/UI:N/VC:L/VI:N/VA:N/SC:L/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.
(20th percentile)

Weaknesses

Improper Handling of Case Sensitivity

The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results. Learn more on MITRE.

Incorrect Authorization

The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. Learn more on MITRE.

CVE ID

CVE-2026-48794

GHSA ID

GHSA-j748-h363-wqj8

Source code

Credits

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