What’s Vulnerable › Vulnerabilities

CVE-2026-3706: mkj Dropbear S Range Check curve25519.c unpackneg signature verification

• Severity: low (CVSS 3.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-08 · updated 2026-06-17
• Weakness: CWE-345

Description

A vulnerability was determined in mkj Dropbear up to 2025.89. Impacted is the function unpackneg of the file src/curve25519.c of the component S Range Check. This manipulation causes improper verification of cryptographic signature. The attack can be initiated remotely. The attack is considered to have high complexity. The exploitability is considered difficult. The actual existence of this vulnerability is currently in question. Patch name: fdec3c90a15447bd538641d85e5a3e3ac981011d. To fix this issue, it is recommended to deploy a patch. The project maintainer explains: "Signature Malleability is not exploitable in SSH protocol. (...) [A] PoC doesn't exist for SSH implementation, but rather it's against the internal API."

Affected products

• mkj Dropbear: 2025.0, 2025.1, 2025.2, 2025.3, 2025.4, 2025.5 (+84)

References

• https://github.com/mkj/dropbear/
• https://github.com/mkj/dropbear/commit/fdec3c90a15447bd538641d85e5a3e3ac981011d
• https://github.com/mkj/dropbear/issues/406
• https://github.com/mkj/dropbear/pull/407
• https://github.com/str4d/ed25519-java/issues/82#issue-727629226
• https://vuldb.com/?ctiid.349652
• https://vuldb.com/?id.349652
• https://vuldb.com/?submit.765933
• https://github.com/mkj/dropbear/issues/406

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