HMAC bypass via global URL signature replacement
Published Jul 31, 2026 · Updated Jul 31, 2026
HMAC validation bypass in thumbor before 7.8.0 allows remote attackers to load unintended domains or paths via crafted signed URLs. In thumbor.handlers.imaging, chained replace() calls remove every plain or URL-encoded copy of the request hash before HMAC verification, so an injected copy changes the resource while reconstructing the signed string. A reachable signed-image endpoint and one valid signature are required; successful exploitation can turn the service into an unauthorized image fetcher.
Summary
What happened
HMAC validation bypass in thumbor before 7.8.0 allows remote attackers to load unintended domains or paths via crafted signed URLs. In thumbor.handlers.imaging, chained replace() calls remove every plain or URL-encoded copy of the request hash before HMAC verification, so an injected copy changes the resource while reconstructing the signed string. A reachable signed-image endpoint and one valid signature are required; successful exploitation can turn the service into an unauthorized image fetcher.
The record
- CVE
- CVE-2026-53501
- Published
- Jul 31, 2026
- Updated
- Jul 31, 2026
- Vendor
- thumbor
- Product
- thumbor
- Classifications
- CWE-347, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 31, 2026CVE publishedPublication date reported by the CVE source.
- Jul 31, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 7.8.0
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
- Crafted duplicate-signature URL examplesproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo