Signature malleability via missing scalar range check
Published Mar 22, 2026 · Updated Mar 22, 2026
Improper Ed25519 signature verification in TinySSH 20250501 allows local users to submit alternate valid signatures. crypto_sign_ed25519_tinyssh_open checks only high bits of the untrusted S scalar, then uses it without enforcing S below subgroup order L, so both S and S+L verify. The built-in non-lib25519 verifier must process a valid signature; the result breaks signature uniqueness and can undermine higher-level policy or audit logic.
Summary
What happened
Improper Ed25519 signature verification in TinySSH 20250501 allows local users to submit alternate valid signatures. crypto_sign_ed25519_tinyssh_open checks only high bits of the untrusted S scalar, then uses it without enforcing S below subgroup order L, so both S and S+L verify. The built-in non-lib25519 verifier must process a valid signature; the result breaks signature uniqueness and can undermine higher-level policy or audit logic.
The record
- CVE
- CVE-2026-4541
- Published
- Mar 22, 2026
- Updated
- Mar 22, 2026
- Vendor
- Jan Mojžíš
- Product
- TinySSH
- Classifications
- CWE-345, CWE-347
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Mar 22, 2026CVE publishedPublication date reported by the CVE source.
- Mar 22, 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=20250501
What conditions does exploitation require?
What is affected?
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
- TinySSH Ed25519 S+L signature malleability PoCproof 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