Authentication bypass via non-constant-time HMAC comparison
Published Feb 25, 2026 · Updated Feb 25, 2026
Observable timing discrepancy in OpenFUN Richie before 3.3.0 allows remote attackers to forge course-sync HMAC signatures via response timing. The sync_course_runs_from_request endpoint compares the Authorization header to expected HMACs with ==, whose early exit leaks matching-prefix length. Repeated unauthenticated requests can recover a valid signature and inject or alter course-run data, public course pages, caches, and the search index.
Summary
What happened
Observable timing discrepancy in OpenFUN Richie before 3.3.0 allows remote attackers to forge course-sync HMAC signatures via response timing. The sync_course_runs_from_request endpoint compares the Authorization header to expected HMACs with ==, whose early exit leaks matching-prefix length. Repeated unauthenticated requests can recover a valid signature and inject or alter course-run data, public course pages, caches, and the search index.
The record
- CVE
- CVE-2026-26717
- Published
- Feb 25, 2026
- Updated
- Feb 25, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-208, CAPEC-580, CAPEC-462, CAPEC-541, T1565.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 25, 2026CVE publishedPublication date reported by the CVE source.
- Feb 25, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
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
- CVE-2026-26717 HMAC timing-attack demonstrationproof of concept · unverified
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Technologies
Your stack
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Your stack
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