Vulnerability-Lookup

CVE-2026-18165 (GCVE-0-2026-18165)

Vulnerability from cvelistv5 – Published: 2026-08-15 13:45 – Updated: 2026-08-17 19:41

Title

@fastify/oauth2 vulnerable to Login CSRF via plantable OAuth state cookies

Summary

@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.

Severity

4.2 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-17 19:41 UTC

CWE

CWE-352 - Cross-Site Request Forgery (CSRF)

Assigner

openjs redhat root

References

2 references

URL	Tags
https://github.com/fastify/fastify-oauth2/securit…
https://cna.openjsf.org/security-advisories.html

Impacted products

1 product

Vendor	Product	Version	CPE status
@fastify/oauth2	@fastify/oauth2	Affected: 7.2.0 , < 8.3.0 (semver) Unaffected: 8.3.0 (semver)	guessed

Credits

kleju13 mcollina UlisesGascon

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-18165

Vulnerability from fkie_nvd - Published: 2026-08-15 14:17 - Updated: 2026-08-17 20:16

Severity

4.2 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

Summary

References

	URL	Tags
	ce714d77-add3-4f53-aff5-83d477b104bb	https://cna.openjsf.org/security-advisories.html
	ce714d77-add3-4f53-aff5-83d477b104bb	https://github.com/fastify/fastify-oauth2/security/advisories/GHSA-p8h8-rj28-m8q9

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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          "defaultStatus": "unaffected",
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            }
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  ],
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  "lastModified": "2026-08-17T20:16:41.040",
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-18165 (GCVE-0-2026-18165)

FKIE_CVE-2026-18165

Tags

Sightings

Nomenclature