Cross-session token exposure via cached proxy fetcher
Published Apr 17, 2026 · Updated Apr 17, 2026
Incorrect authorization in Auth0 Next.js SDK 4.12.0 through 4.17.1 allows remote authenticated users to receive a different session's token. The proxy handler caches a request-bound Fetcher by domain and audience, then mutates its token callback, allowing concurrent nonce retries to resolve against a different session. Exploitation requires concurrent profile or organization proxy requests with DPoP enabled and user interaction; the mismatched token exposes protected account data and enables limited unauthorized changes.
Summary
What happened
Incorrect authorization in Auth0 Next.js SDK 4.12.0 through 4.17.1 allows remote authenticated users to receive a different session's token. The proxy handler caches a request-bound Fetcher by domain and audience, then mutates its token callback, allowing concurrent nonce retries to resolve against a different session. Exploitation requires concurrent profile or organization proxy requests with DPoP enabled and user interaction; the mismatched token exposes protected account data and enables limited unauthorized changes.
The record
- CVE
- CVE-2026-40155
- Published
- Apr 17, 2026
- Updated
- Apr 17, 2026
- Vendor
- Auth0
- Product
- Auth0 Next.js SDK
- Classifications
- CWE-863, CWE-362, T1528
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 17, 2026CVE publishedPublication date reported by the CVE source.
- Apr 17, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 4.12.0, < 4.18.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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