CVE-2026-3706
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."
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
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 Medium
CVSS: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 Low
CVSS: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 Low
CVSS: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 Medium
CVSS: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 Low
CVSS: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 Low
CVSS: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 Low
CVSS: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 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N - CVSS 2.0
- 2.6 Low
AV: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 Low
CVSS: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 Low
CVSS: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 Low
CVSS: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 Low
CVSS: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
| Package | Affected | Fixed |
|---|---|---|
dropbearDebian: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 less2022.83-22022.83-32022.83-42024.84-12024.85-12024.85-22024.85-32024.86-12024.86-22025.87-12025.88-12025.88-22025.89-12025.89-1~deb13u12026.90-12026.91-12026.92-12026.93-12026.94-1 |
None known |
dropbearDebian: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 |
dropbearDebian:14 |
before 2026.90-1, plus listed versions 2025.88-22025.89-12025.89-1~deb13u1 |
2026.90-1 |
dropbearUbuntu:16.04:LTS |
All versions, plus listed versions 2014.65-1ubuntu22015.68-12015.70-12015.71-12016.72-1 |
None known |
dropbearUbuntu:Pro:18.04:LTS |
All versions, plus listed versions 2017.75-22017.75-3build12017.75-3ubuntu0.1~esm1 |
None known |
dropbearUbuntu:Pro:20.04:LTS |
All versions, plus listed versions 2019.78-2build12019.78-2ubuntu0.1~esm1 |
None known |
dropbearUbuntu:22.04:LTS |
All versions, plus listed versions 2020.81-32020.81-42020.81-52020.81-5ubuntu0.1 |
None known |
dropbearUbuntu:24.04:LTS |
All versions, plus listed versions 2022.83-22022.83-32022.83-4 |
None known |
dropbearUbuntu:25.10 |
All versions, plus listed versions 2024.86-22025.88-2 |
None known |
dropbearUbuntu:26.10 |
All versions, plus listed versions 2025.89-12026.91-12026.92-12026.94-12026.94-1ubuntu1 |
None known |
dropbearUbuntu:26.04:LTS |
All versions, plus listed versions 2025.88-22025.89-1 |
None known |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE 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
vuldb.com?id.349652
vuldb.com?ctiid.349652
vuldb.com?submit.765933
github.com/mkj/dropbear/issues/406
github.com/mkj/dropbear/pull/407
github.com/mkj/dropbear/commit/fdec3c90a15447bd538641d85e5a3e3ac981011d
Show 8 moreShow less
github.com/str4d/ed25519-java/issues/82
github.com/mkj/dropbear
nvd.nist.gov/vuln/detail/CVE-2026-3706
github.com/advisories/GHSA-87g2-jprq-4cmc
github.com/CVEProject/cvelistV5/tree/main/cves/2026/3xxx/CVE-2026-3706.json
security-tracker.debian.org/tracker/CVE-2026-3706
ubuntu.com/security/CVE-2026-3706
cve.org/CVERecord?id=CVE-2026-3706