CVE-2026-3706 Details
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."
A vulnerability exists in mkj Dropbear SSH server software in versions through 2025.89. The issue is located in the Curve25519 implementation, specifically within the 'unpackneg' function of 'src/curve25519.c'. This vulnerability arises from an improper range check on the 'S' value of Ed25519 signatures, allowing for signature malleability. The flaw can be exploited remotely, with a public proof-of-concept available.
Users are advised to apply the patch available in the commit 'fdec3c90a15447bd538641d85e5a3e3ac981011d'.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Mar 8, 2026CISA-ADP
Assessed Mar 10, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/mkj/dropbear/issues/406 | CISA-ADP | |
| https://github.com/mkj/dropbear/ | [email protected] | ProductSource CodeVendor |
| https://github.com/mkj/dropbear/commit/fdec3c90a15447bd538641d85e5a3e3ac981011d | [email protected] | Source CodeVendor |
| https://github.com/mkj/dropbear/issues/406 | [email protected] | |
| https://github.com/mkj/dropbear/pull/407 | [email protected] | Issue TrackingVendor |
| https://github.com/str4d/ed25519-java/issues/82#issue-727629226 | [email protected] | Issue TrackingTechnical Description |
| https://vuldb.com/?ctiid.349652 | [email protected] | AdvisoryPermission Required |
| https://vuldb.com/?id.349652 | [email protected] | AdvisoryExploitRemedy |
| https://vuldb.com/?submit.765933 | [email protected] | Technical Description |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-345 | Insufficient Verification of Data Authenticity | [email protected] |
| CWE-347 | Improper Verification of Cryptographic Signature | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| mkj Dropbear | <= 2025.89 |
CPE
Remediation
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Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Apr 22, 2026 | CVE Modified | CISA-ADP |
| Mar 16, 2026 | CVE Modified | [email protected] |
| Mar 8, 2026 | New CVE Received | [email protected] |