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Craft CMS: Passkey login accepts replayed WebAuthn assertions

Critical severity GitHub Reviewed Published Jul 25, 2026 in craftcms/cms • Updated Aug 7, 2026

Package

composer craftcms/cms (Composer)

Affected versions

>= 5.0.0-RC1, < 5.10.5

Patched versions

5.10.5

Description

Craft CMS passkey login accepts WebAuthn requestOptions from the unauthenticated login request body and does not persist the updated credential counter returned by the WebAuthn assertion validator. A captured passkey login request body can therefore be replayed because the old challenge is accepted again, and the stored credential counter remains stale.

Craft CMS 5.10.3 and current 5.x HEAD accept PublicKeyCredentialRequestOptions from the unauthenticated users/login-with-passkey request body and do not persist the updated PublicKeyCredentialSource returned/mutated by web-auth/webauthn-lib after assertion validation.

As a result, a captured passkey login request body is not one-time-use. Reposting the same requestOptions and response can result in validation against the same stale credential counter and create another Craft session for that user. This weakens passkeys from a fresh, server-challenged authentication ceremony into a replayable bearer artifact if one successful assertion body is exposed.

Attack Scenario

  1. A victim successfully logs in with a passkey.
  2. The POST /actions/users/login-with-passkey body containing requestOptions and response is captured from an application/request log, debugging proxy, browser extension, compromised analytics layer, or another request-body disclosure point.
  3. The attacker reposts the same body to users/login-with-passkey.
  4. Craft deserializes the attacker-supplied requestOptions, so the old challenge remains accepted for validation.
  5. The WebAuthn validator compares the assertion's signCount against the stale stored credential counter.
  6. Because Craft did not persist the updated credential source on the original login, the same stale stored counter is used again.
  7. The same captured assertion validates and Craft creates another authenticated session for the victim account.

This is exactly what WebAuthn's challenge and signature-counter lifecycle is meant to prevent: a successful assertion should be bound to a server-issued challenge and should update server-side credential state so it cannot be used again.

Impact

An attacker who obtains one successful passkey login request body can replay it to create additional authenticated Craft sessions for that user. This defeats WebAuthn’s intended one-time challenge and signature-counter replay protection, reducing a passkey assertion to a reusable bearer artifact if exposed through request logging, a debugging proxy, a compromised same-origin script layer, or another request-body disclosure path.

The impact is an account/session takeover of the affected passkey account after a single assertion body is captured. The issue is in Craft’s native passkey login flow and affects fresh Craft installations with passkeys enabled.

References

@angrybrad angrybrad published to craftcms/cms Jul 25, 2026
Published to the GitHub Advisory Database Aug 7, 2026
Reviewed Aug 7, 2026
Last updated Aug 7, 2026

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 Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
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:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Authentication Bypass by Capture-replay

A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes). Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-wg23-69c2-gjc8

Source code

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