fastify fastify-oauth2 up to 8.2.x cross-site request forgery

Summaryinfo

A vulnerability has been found in fastify fastify-oauth2 up to 8.2.x and classified as problematic. Affected is an unknown function. Performing a manipulation results in cross-site request forgery. This vulnerability is cataloged as CVE-2026-18165. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in fastify fastify-oauth2 up to 8.2.x. It has been classified as problematic. This affects an unknown part. The manipulation with an unknown input leads to a cross-site request forgery vulnerability. CWE is classifying the issue as CWE-352. The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request. This is going to have an impact on integrity. The summary by CVE is:

@fastify/oauth2 is an OAuth 2.0 plugin for Fastify. In versions from 7.2.0 up to but not including 8.3.0, the plugin validates the OAuth state, and with PKCE the code verifier, by comparing the callback query parameter against an unprefixed, predictable cookie, with no server-side binding to the browser that began the flow. Any party able to write a cookie for the application's host, such as a sibling subdomain under the same registrable domain, can plant matching state and verifier cookies and complete an attacker-owned OAuth flow inside a victim's browser, silently signing the victim in to the attacker's account (login CSRF). It does not expose the victim's own account, credentials, or tokens. The issue is fixed in @fastify/oauth2 8.3.0, which adds an opt-in hostPrefixedCookies option. Users should upgrade to 8.3.0 and enable it, or bind state to a server-side session.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-18165 since 07/28/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 8.3.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-59767). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

• fastify

Name

• fastify-oauth2

Version

• 8.0
• 8.1
• 8.2

Website

• Product: https://github.com/fastify/fastify-oauth2/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Discussion