Evidence used
- No CISA KEV confirmation is currently recorded.
- EPSS is 0.10% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-18165High confidence
@fastify/oauth2 vulnerable to Login CSRF via plantable OAuth state cookies
@fastify/oauth2 · @fastify/oauth2
Official source article: GitHub GHSA-P8H8-RJ28-M8Q9 ↗. Check the applicable product and release in the original source.
4.2MediumCVSS 3.1
Patch only the product branches with a verified fix
Fix availability varies by productMedium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityMedium→Operational priority:Medium, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs @fastify/oauth2 @fastify/oauth2 and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Remediation availability differs by product scope
Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
- Red Hat Product Security: 1 affected or under-investigation product state without a fixed product state in the same current advisory
Direct vendor intelligence
1 currentAuthoritative vendor CSAF and VEX advisories
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
CVE-2026-18165 · CSAF 2.0 · revision 3 · finalRed Hat Product Security@fastify/oauth2: @fastify/oauth2: Login CSRF via predictable OAuth state cookies
The vendor explicitly identifies these products as affected by this CVE.
- devspaces/dashboard-rhel9 as a component of Red Hat OpenShift Dev Spaces
- Summary
- A flaw was found in @fastify/oauth2, an OAuth 2.0 plugin for Fastify. This vulnerability allows a remote attacker to perform a Login Cross-Site Request Forgery (CSRF) attack. By planting predictable OAuth state and code verifier cookies, an attacker can trick a victim's browser into completing an attacker-controlled OAuth flow. This results in the victim being silently signed into the attacker's account, though it does not expose the victim's own credentials or tokens.
- Remediation
- This issue is fixed in @fastify/oauth2 version 8.3.0. Red Hat will provide updated versions of OpenShift Dev Spaces that include the fixed library version. Until updates are available, administrators can reduce the risk of login CSRF attacks by implementing the following mitigations: 1. Isolate OpenShift Dev Spaces instances on dedicated domains or subdomains that do not share registrable domains with untrusted applications or user-controlled content. 2. If server-side session management is available, bind OAuth state parameters to server-side sessions rather than relying solely on cookie-based state validation. 3. Monitor for suspicious OAuth flows, particularly cases where users appear to be signed into unexpected accounts or workspaces they did not create. 4. Educate developers about the risks of using OAuth login links from untrusted sources, and encourage verification of account identity after OAuth login completes. 5. When upgrading to @fastify/oauth2 8.3.0 or later, enable the hostPrefixedCookies option to prevent cross-subdomain cookie planting attacks. Note that this vulnerability requires the attacker to control a sibling subdomain or exploit a cross-site scripting vulnerability on a sibling subdomain, which significantly raises the attack complexity in most deployment scenarios.
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 1 structured product or package state remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Fix availability varies by product01
What, why and how
@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.
What
@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.
Why
The application accepts a state-changing browser request without a reliable anti-forgery check.
How
An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
@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.
Why
The application accepts a state-changing browser request without a reliable anti-forgery check.
How
An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
- Likely attack path
- a network path → Cross-Site Request Forgery (CSRF) → cause the confidentiality, integrity or availability impact described by the vendor
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- Required interaction required
- Attack complexity
- High: exploitation depends on specific conditions
- Security boundary
- Unchanged: impact remains within the vulnerable component's security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-352 ↗
CWE-352: Cross-Site Request Forgery (CSRF). The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:NCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SUnchangedScope: The security impact remains within the vulnerable component's authority.CLowConfidentiality impact: A successful attack can cause a limited loss.ILowIntegrity impact: A successful attack can cause a limited loss.ANoneAvailability impact: No direct loss is represented by this metric.- Post-exploitation / living off the land
- Stolen credentials, tokens and legitimate administration functions may provide continued access without deploying a large custom toolset.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Fix availability varies by product
- Action
- Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
- Workaround
- This issue is fixed in @fastify/oauth2 version 8.3.0. Red Hat will provide updated versions of OpenShift Dev Spaces that include the fixed library version. Until updates are available, administrators can reduce the risk of login CSRF attacks by implementing the following mitigations: 1. Isolate OpenShift Dev Spaces instances on dedicated domains or subdomains that do not share registrable domains with untrusted applications or user-controlled content. 2. If server-side session management is available, bind OAuth state parameters to server-side sessions rather than relying solely on cookie-based state validation. 3. Monitor for suspicious OAuth flows, particularly cases where users appear to be signed into unexpected accounts or workspaces they did not create. 4. Educate developers about the risks of using OAuth login links from untrusted sources, and encourage verification of account identity after OAuth login completes. 5. When upgrading to @fastify/oauth2 8.3.0 or later, enable the hostPrefixedCookies option to prevent cross-subdomain cookie planting attacks. Note that this vulnerability requires the attacker to control a sibling subdomain or exploit a cross-site scripting vulnerability on a sibling subdomain, which significantly raises the attack complexity in most deployment scenarios.
Official vendor articles1 stored document
Linked articles are downloaded and versioned as source evidence. A CVE mention or approved update relationship does not, by itself, verify a fix for every product branch.
- @fastify/oauth2 vulnerable to Login CSRF via plantable OAuth state cookies · Advisory · fastify/fastify-oauth2 · GitHub →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026fastify / fastify-oauth2 Public Uh oh! There was an error while loading. Please reload this page . Notifications You must be signed in to change notification settings Fork 74 Star 319 Code Issues 7 Pull requests 2 Actions Security and quality 2 Insights Additional navigation options Code Issues Pull req
04
Evidence and provenance
Published 15 Aug 2026 · Last source change 17 Aug 2026, 19:41 UTC · CWE-352 · Cross-Site Request Forgery (CSRF)
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-23
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-59767
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- Vendor guidanceAuthoritative vendor guidance changed: added mitigation: github.com/GHSA-p8h8-rj28-m8q9; added vendor advisory: cna.openjsf.org/security-advisories.html.github.com ↗
- Before
- remediation: github.com/GHSA-p8h8-rj28-m8q9
- After
- mitigation: github.com/GHSA-p8h8-rj28-m8q9 · remediation: github.com/GHSA-p8h8-rj28-m8q9 · vendor advisory: cna.openjsf.org/security-advisories.html
- Catalogue recordCVE added to the BlackTree catalogue.CNA ↗
CVE published
Fixed release or patch reference recorded
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.