CSRF bypass via malformed expected token
Published Dec 27, 2022 · Updated Apr 11, 2025
Improper input validation in nosurf before 1.1.1 allows remote attackers to bypass CSRF protection with arbitrary tokens. VerifyToken ignores Base64 decoding errors and compares zero-length decoded values as equal instead of rejecting malformed expected tokens. Exposure requires an integration that supplies an attacker-influenced or otherwise malformed expected token, enabling unauthorized state-changing requests.
Summary
What happened
Improper input validation in nosurf before 1.1.1 allows remote attackers to bypass CSRF protection with arbitrary tokens. VerifyToken ignores Base64 decoding errors and compares zero-length decoded values as equal instead of rejecting malformed expected tokens. Exposure requires an integration that supplies an attacker-influenced or otherwise malformed expected token, enabling unauthorized state-changing requests.
The record
- CVE
- CVE-2020-36564
- Published
- Dec 27, 2022
- Updated
- Apr 11, 2025
- Vendor
- justinas
- Product
- nosurf
- Classifications
- CWE-20, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Dec 27, 2022CVE publishedPublication date reported by the CVE source.
- Apr 11, 2025Record 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=0 <1.1.1
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.
Public exploit references
- VerifyToken false-positive proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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