CVE-2026-3706: mkj Dropbear S Range Check curve25519.c unpackneg signature verification
Vulnerability summary
CVE-2026-3706 is a medium (CVSS 6.3) vulnerability in mkj dropbear. EPSS estimates a 0.18% chance of exploitation in the next 30 days, higher than 7.8% of scored vulnerabilities.
Not severe (CVSS 6.3, network access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Timeline
- 08-03-2026PublishedVulnerability first disclosed.
- 22-04-2026Last modifiedVulnerability information updated.
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."
CVSS metrics
10 scores · 4 sources · 4 versions- OSV · UbuntuEcosystem advisory · calculated6.3MediumCVSS: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
- OSV · DebianEcosystem advisory · calculated6.3MediumCVSS: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
- NVDNIST1.7LowCVSS: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:XDiffers
- OSV · UbuntuEcosystem advisory · calculated3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- NVDNIST3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- NVDNIST2.6LowAV:N/AC:H/Au:N/C:N/I:P/A:N
EPSS trend
Probability
0.18%
Chance of exploitation in the next 30 days
Percentile
8%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.18% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-345Insufficient Verification of Data AuthenticityThe product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
- CWE-347Improper Verification of Cryptographic SignatureThe product does not verify, or incorrectly verifies, the cryptographic signature for data.
Affected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Debian1 product
- dropbearAll versions (No fix recorded) | < 2026.90-1
Mkj1 product
- dropbear2025.0 | 2025.1 | 2025.2 | 2025.3 | 2025.4 | 2025.5 | 2025.6 | 2025.7 | 2025.8 | 2025.9 | 2025.10 | 2025.11 | 2025.12 | 2025.13 | 2025.14 | 2025.15 | 2025.16 | 2025.17 | 2025.18 | 2025.19 | 2025.20 | 2025.21 | 2025.22 | 2025.23 | 2025.24 | 2025.25 | 2025.26 | 2025.27 | 2025.28 | 2025.29 | 2025.30 | 2025.31 | 2025.32 | 2025.33 | 2025.34 | 2025.35 | 2025.36 | 2025.37 | 2025.38 | 2025.39 | 2025.40 | 2025.41 | 2025.42 | 2025.43 | 2025.44 | 2025.45 | 2025.46 | 2025.47 | 2025.48 | 2025.49 | 2025.50 | 2025.51 | 2025.52 | 2025.53 | 2025.54 | 2025.55 | 2025.56 | 2025.57 | 2025.58 | 2025.59 | 2025.60 | 2025.61 | 2025.62 | 2025.63 | 2025.64 | 2025.65 | 2025.66 | 2025.67 | 2025.68 | 2025.69 | 2025.70 | 2025.71 | 2025.72 | 2025.73 | 2025.74 | 2025.75 | 2025.76 | 2025.77 | 2025.78 | 2025.79 | 2025.80 | 2025.81 | 2025.82 | 2025.83 | 2025.84 | 2025.85 | 2025.86 | 2025.87 | 2025.88 | 2025.89
Ubuntu1 product
- dropbearAll versions (No fix recorded)
3 vendors · 3 products
