Signature malleability via missing Ed25519 range check
Published Mar 8, 2026 · Updated Mar 8, 2026
Ed25519 signature malleability in Dropbear SSH 2025.89 and earlier allows attackers to produce alternate signatures via noncanonical S values. The dropbear_ed25519_verify function in src/curve25519.c accepts S values at or above group order L, so adding L to a valid signature yields a second accepted encoding. Exploitation requires a valid signature to transform, and the maintainer disputes SSH-protocol impact because the proof of concept exercises only the internal API.
Summary
What happened
Ed25519 signature malleability in Dropbear SSH 2025.89 and earlier allows attackers to produce alternate signatures via noncanonical S values. The dropbear_ed25519_verify function in src/curve25519.c accepts S values at or above group order L, so adding L to a valid signature yields a second accepted encoding. Exploitation requires a valid signature to transform, and the maintainer disputes SSH-protocol impact because the proof of concept exercises only the internal API.
The record
- CVE
- CVE-2026-3706
- Published
- Mar 8, 2026
- Updated
- Mar 8, 2026
- Vendor
- Dropbear SSH Project
- Product
- Dropbear SSH
- Classifications
- CWE-347, CWE-345
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Mar 8, 2026CVE publishedPublication date reported by the CVE source.
- Mar 8, 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=2025.0
- Affected versionversion=2025.1
- Affected versionversion=2025.10
- Affected versionversion=2025.11
- Affected versionversion=2025.12
- Affected versionversion=2025.13
- Affected versionversion=2025.14
- Affected versionversion=2025.15
- Affected versionversion=2025.16
- Affected versionversion=2025.17
- Affected versionversion=2025.18
- Affected versionversion=2025.19
- Affected versionversion=2025.2
- Affected versionversion=2025.20
- Affected versionversion=2025.21
- Affected versionversion=2025.22
- Affected versionversion=2025.23
- Affected versionversion=2025.24
- Affected versionversion=2025.25
- Affected versionversion=2025.26
- Affected versionversion=2025.27
- Affected versionversion=2025.28
- Affected versionversion=2025.29
- Affected versionversion=2025.3
- Affected versionversion=2025.30
- Affected versionversion=2025.31
- Affected versionversion=2025.32
- Affected versionversion=2025.33
- Affected versionversion=2025.34
- Affected versionversion=2025.35
- Affected versionversion=2025.36
- Affected versionversion=2025.37
- Affected versionversion=2025.38
- Affected versionversion=2025.39
- Affected versionversion=2025.4
- Affected versionversion=2025.40
- Affected versionversion=2025.41
- Affected versionversion=2025.42
- Affected versionversion=2025.43
- Affected versionversion=2025.44
- Affected versionversion=2025.45
- Affected versionversion=2025.46
- Affected versionversion=2025.47
- Affected versionversion=2025.48
- Affected versionversion=2025.49
- Affected versionversion=2025.5
- Affected versionversion=2025.50
- Affected versionversion=2025.51
- Affected versionversion=2025.52
- Affected versionversion=2025.53
- Affected versionversion=2025.54
- Affected versionversion=2025.55
- Affected versionversion=2025.56
- Affected versionversion=2025.57
- Affected versionversion=2025.58
- Affected versionversion=2025.59
- Affected versionversion=2025.6
- Affected versionversion=2025.60
- Affected versionversion=2025.61
- Affected versionversion=2025.62
- Affected versionversion=2025.63
- Affected versionversion=2025.64
- Affected versionversion=2025.65
- Affected versionversion=2025.66
- Affected versionversion=2025.67
- Affected versionversion=2025.68
- Affected versionversion=2025.69
- Affected versionversion=2025.7
- Affected versionversion=2025.70
- Affected versionversion=2025.71
- Affected versionversion=2025.72
- Affected versionversion=2025.73
- Affected versionversion=2025.74
- Affected versionversion=2025.75
- Affected versionversion=2025.76
- Affected versionversion=2025.77
- Affected versionversion=2025.78
- Affected versionversion=2025.79
- Affected versionversion=2025.8
- Affected versionversion=2025.80
- Affected versionversion=2025.81
- Affected versionversion=2025.82
- Affected versionversion=2025.83
- Affected versionversion=2025.84
- Affected versionversion=2025.85
- Affected versionversion=2025.86
- Affected versionversion=2025.87
- Affected versionversion=2025.88
- Affected versionversion=2025.89
- Affected versionversion=2025.9
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
- Dropbear Ed25519 S+L verification 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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