Every CVE Search/ Get API key

CVE-2026-3706

mkj Dropbear S Range Check curve25519.c unpackneg signature verification

6.3 MediumFix availableDisputed

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."

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
Low
Availability
None

Exploit likelihood

0.18%Up 0.2 points since Mar 8, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.3

mkj Dropbear S Range Check curve25519.c unpackneg signature verification

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."

Record
CVE-2026-3706
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U
CVSS 3.1
3.7 LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N/E:U/RL:O/RC:C
CVSS 3.0
3.7 LowCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N/E:U/RL:O/RC:C
CVSS 2.0
2.6 AV:N/AC:H/Au:N/C:N/I:P/A:N/E:U/RL:OF/RC:C
Weakness
CWE-347, CWE-345
Updated
2026-11-02
EUVDEUVD-2026-10213 6.3

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."

Record
EUVD-2026-10213
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U
Updated
2026-11-02
GitHub AdvisoriesGHSA-87g2-jprq-4cmc 2.9

A vulnerability was determined in mkj Dropbear up to 2025.89. Impacted is the function unpackneg...

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 exploit has been publicly disclosed and may be utilized. Patch name: fdec3c90a15447bd538641d85e5a3e3ac981011d. To fix this issue, it is recommended to deploy a patch.

Record
GHSA-87g2-jprq-4cmc
CVSS 4.0
2.9 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1
3.7 LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-345
Updated
2026-11-02
NVD 1.7

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."

Record
CVE-2026-3706
CVSS 4.0
1.7 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1
3.7 LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
CVSS 2.0
2.6 LowAV:N/AC:H/Au:N/C:N/I:P/A:N
Weakness
CWE-345, CWE-347
Updated
2026-11-02
OSV 1.7

mkj Dropbear S Range Check curve25519.c unpackneg signature verification

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."

Record
CVE-2026-3706
CVSS 4.0
1.7 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U
Weakness
CWE-345, CWE-347
Updated
2026-11-02
OSVDEBIAN-CVE-2026-3706 1.7

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."

Record
DEBIAN-CVE-2026-3706
CVSS 4.0
1.7 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Updated
2026-11-02
OSVUBUNTU-CVE-2026-3706 1.7

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."

Record
UBUNTU-CVE-2026-3706
CVSS 4.0
1.7 LowCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U
CVSS 3.1
3.7 LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
dropbear
Debian:12
All versions, plus listed versions
2022.83-12022.83-1+deb12u12022.83-1+deb12u1~bpo11+12022.83-1+deb12u22022.83-1+deb12u3
Show 19 moreShow less
2022.83-22022.83-32022.83-42024.84-12024.85-12024.85-22024.85-32024.86-12024.86-22025.87-12025.88-12025.88-22025.89-12025.89-1~deb13u12026.90-12026.91-12026.92-12026.93-12026.94-1
None known
dropbear
Debian:13
All versions, plus listed versions
2025.88-22025.89-12025.89-1~deb13u12026.90-12026.91-12026.92-12026.93-12026.94-1
None known
dropbear
Debian:14
before 2026.90-1, plus listed versions
2025.88-22025.89-12025.89-1~deb13u1
2026.90-1
dropbear
Ubuntu:16.04:LTS
All versions, plus listed versions
2014.65-1ubuntu22015.68-12015.70-12015.71-12016.72-1
None known
dropbear
Ubuntu:Pro:18.04:LTS
All versions, plus listed versions
2017.75-22017.75-3build12017.75-3ubuntu0.1~esm1
None known
dropbear
Ubuntu:Pro:20.04:LTS
All versions, plus listed versions
2019.78-2build12019.78-2ubuntu0.1~esm1
None known
dropbear
Ubuntu:22.04:LTS
All versions, plus listed versions
2020.81-32020.81-42020.81-52020.81-5ubuntu0.1
None known
dropbear
Ubuntu:24.04:LTS
All versions, plus listed versions
2022.83-22022.83-32022.83-4
None known
dropbear
Ubuntu:25.10
All versions, plus listed versions
2024.86-22025.88-2
None known
dropbear
Ubuntu:26.10
All versions, plus listed versions
2025.89-12026.91-12026.92-12026.94-12026.94-1ubuntu1
None known
dropbear
Ubuntu:26.04:LTS
All versions, plus listed versions
2025.88-22025.89-1
None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-3706 is a medium vulnerability (CVSS 6.3) in Mkj Dropbear, published March 8, 2026. Its validity is disputed. EPSS puts the chance of exploitation in the next 30 days at 0.18%, the 7th percentile. Fixed in dropbear 2026.90-1.

References

Show 8 moreShow less
MoveEnter Open