The diffie_hellman_sha256 function in kex.c in libssh2 before 1.7.0 improperly truncates secrets to 128 or 256 bits, which makes it easier f
The diffie_hellman_sha256 function in kex.c in libssh2 before 1.7.0 improperly truncates secrets to 128 or 256 bits, which makes it easier for man-in-the-middle attackers to decrypt or intercept SSH sessions via unspecified vectors, aka a "bits/bytes confusion bug."
- Published
- Apr 13, 2016
- Updated
- Jun 16, 2026
- EPSS
- 2.6% · 85th percentile
- CWE
- CWE-200
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Report tools
Action score
24
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 1 / 30 · 2.6%
Affected systems
| Vendor | Product | CPE |
|---|---|---|
| libssh2 | libssh2 | cpe:2.3:a:libssh2:libssh2 |
| fedoraproject | fedora | cpe:2.3:o:fedoraproject:fedora |
| opensuse | opensuse | cpe:2.3:o:opensuse:opensuse |
| debian | debian linux | cpe:2.3:o:debian:debian_linux |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- debian debian linux7.0
- debian debian linux8.0
- fedoraproject fedora22
- fedoraproject fedora23
- libssh2 libssh2up to 1.6.0 inclusive
- opensuse opensuse13.2
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Alpine:v3.4 | libssh2 | before 1.7.0-r0 | 1.7.0-r0 |
| Debian:12 | libssh2 | before 1.5.0-2.1 | 1.5.0-2.1 |
| Debian:6.0 | libssh2 | before 1.2.6-1+deb6u2 | 1.2.6-1+deb6u2 |
| Debian:7 | libssh2 | before 1.4.2-1.1+deb7u2 | 1.4.2-1.1+deb7u2 |
| Debian:8 | libssh2 | before 1.4.3-4.1+deb8u1 | 1.4.3-4.1+deb8u1 |
| openSUSE:Tumbleweed | libssh2_org | before 1.7.0-1.5 | 1.7.0-1.5 |
| Red Hat:enterprise_linux:6::client | libssh2 | before 0:1.4.2-2.el6_7.1 | 0:1.4.2-2.el6_7.1 |
| Red Hat:enterprise_linux:6::client | libssh2-debuginfo | before 0:1.4.2-2.el6_7.1 | 0:1.4.2-2.el6_7.1 |
| Red Hat:enterprise_linux:6::client | libssh2-devel | before 0:1.4.2-2.el6_7.1 | 0:1.4.2-2.el6_7.1 |
| Red Hat:enterprise_linux:6::client | libssh2-docs | before 0:1.4.2-2.el6_7.1 | 0:1.4.2-2.el6_7.1 |
| Red Hat:enterprise_linux:7::client | libssh2 | before 0:1.4.3-10.el7_2.1 | 0:1.4.3-10.el7_2.1 |
| Red Hat:enterprise_linux:7::client | libssh2-debuginfo | before 0:1.4.3-10.el7_2.1 | 0:1.4.3-10.el7_2.1 |
| Red Hat:enterprise_linux:7::client | libssh2-devel | before 0:1.4.3-10.el7_2.1 | 0:1.4.3-10.el7_2.1 |
| Red Hat:enterprise_linux:7::client | libssh2-docs | before 0:1.4.3-10.el7_2.1 | 0:1.4.3-10.el7_2.1 |
| SUSE:Linux Enterprise Desktop 12 | libssh2_org | before 1.4.3-16.1 | 1.4.3-16.1 |
| SUSE:Linux Enterprise Software Development Kit 11 SP4 | libssh2_org | before 1.2.9-4.2.6.1 | 1.2.9-4.2.6.1 |
Same product
libssh2: all recordsOther highest-scoring records for the same primary product.
- CVE-2019-3861An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the way SSH packets with a padding length value greater than the packet38Monitor
- CVE-2019-3860An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the way SFTP packets with empty payloads are parsed.38Monitor
- CVE-2019-3858An out of bounds read flaw was discovered in libssh2 before 1.8.1 when a specially crafted SFTP packet is received from the server.38Monitor
- CVE-2019-3855An integer overflow flaw which could lead to an out of bounds write was discovered in libssh2 before 1.8.1 in the way packets are read from 38Monitor
- CVE-2019-3862An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the way SSH_MSG_CHANNEL_REQUEST packets with an exit status message and38Monitor
- CVE-2019-3859An out of bounds read flaw was discovered in libssh2 before 1.8.1 in the _libssh2_packet_require and _libssh2_packet_requirev functions.38Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| alpine:libssh2 | 1.7.0-r0 · Alpine:v3.4 | Package registry (OSV) |
| debian:libssh2 | 1.5.0-2.1 · Debian:12 | Package registry (OSV) |
| opensuse:libssh2_org | 1.7.0-1.5 · openSUSE:Tumbleweed | Package registry (OSV) |
| red hat:libssh2 | 0:1.4.2-2.el6_7.1 · Red Hat:enterprise_linux:6::client | Package registry (OSV) |
| red hat:libssh2-debuginfo | 0:1.4.2-2.el6_7.1 · Red Hat:enterprise_linux:6::client | Package registry (OSV) |
| red hat:libssh2-devel | 0:1.4.2-2.el6_7.1 · Red Hat:enterprise_linux:6::client | Package registry (OSV) |
| red hat:libssh2-docs | 0:1.4.2-2.el6_7.1 · Red Hat:enterprise_linux:6::client | Package registry (OSV) |
| suse:libssh2_org | 1.4.3-16.1 · SUSE:Linux Enterprise Desktop 12 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- high · data can be read
- Integrity
- none
- Availability
- none
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- None
- Availability impact
- None
Weakness class (CWE)
CWE-200 · Exposure of Sensitive Information to an Unauthorized ActorCVSS vector
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
nvd-primary
Root cause
The extension requests broader permissions than its function needs and sends the data it collects out for purposes beyond its stated function.
The bug in code
The whole CWE-200 classA representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.
Vulnerable
{ "permissions": ["tabs", "<all_urls>"], "background": { "service_worker": "analytics.js" }}Fixed
{ "permissions": ["activeTab"], "host_permissions": ["https://yildiz.example/*"]}Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- ExcavationCAPEC-116likelihood: High · Medium
- Subverting Environment Variable ValuesCAPEC-13likelihood: High · Very High
- FootprintingCAPEC-169likelihood: High · Very Low
- Exploiting Trust in ClientCAPEC-22likelihood: High · High
- FingerprintingCAPEC-224likelihood: High · Very Low
- ICMP Echo Request PingCAPEC-285likelihood: Medium · Low
- TCP SYN ScanCAPEC-287Low
- Enumerate Mail Exchange (MX) RecordsCAPEC-290Low
ATT&CK techniques
- System Service DiscoveryT1007
- System Network Configuration DiscoveryT1016
- Remote System DiscoveryT1018
- System Owner/User DiscoveryT1033
- Masquerading: Match Legitimate Name or LocationT1036.005
- Network Service ScanningT1046
- System Network Connections DiscoveryT1049
- Process DiscoveryT1057
- Permission Groups DiscoveryT1069
- System Information DiscoveryT1082
- File and Directory DiscoveryT1083
- Account DiscoveryT1087
- Multi-Factor Authentication InterceptionT1111
- Peripheral Device DiscoveryT1120
- System Time DiscoveryT1124
- Access Token Manipulation:Token Impersonation/TheftT1134.001
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpChange log
- Fix✗ → ✓
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References
- lists.fedoraproject.org/pipermail/package-announce/2016-February/177980.html
- lists.fedoraproject.org/pipermail/package-announce/2016-March/178573.html
- lists.opensuse.org/opensuse-updates/2016-03/msg00008.html
- www.debian.org/security/2016/dsa-3487
- www.oracle.com/technetwork/topics/security/linuxbulletinjan2016-2867209.html
- www.securityfocus.com/bid/82514
- bto.bluecoat.com/security-advisory/sa120
- kc.mcafee.com/corporate/index?page=content&id=SB10156
- puppet.com/security/cve/CVE-2016-0787
- security.gentoo.org/glsa/201606-12
- www.libssh2.org/CVE-2016-0787.patch
- www.libssh2.org/adv_20160223.html
Vendor advisories and official records. Exploit/PoC links are deliberately left out.