CVE catalog
CVE-2021-3634
libssh: CVE-2021-3634
- Severity
- Low · CVSS 3.5
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:L - Published
- Source
- [NVD] · [CVE record]
- EPSS
- 4.68% · Oct 25, 2026
A flaw has been found in libssh in versions prior to 0.9.6. The SSH protocol keeps track of two shared secrets during the lifetime of the session. One of them is called secret_hash and the other session_id. Initially, both of them are the same, but after key re-exchange, previous session_id is kept and used as an input to new secret_hash. Historically, both of these buffers had shared length variable, which worked as long as these buffers were same. But the key re-exchange operation can also change the key exchange method, which can be based on hash of different size, eventually creating "secret_hash" of different size than the session_id has. This becomes an issue when the session_id memory is zeroed or when it is used again during second key re-exchange.
Vulnerable and fixed packages
Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.
| Distribution | Package | Release | Version | Status |
|---|---|---|---|---|
| Debian | libssh | sid | 0.12.2-1 | fixed |
| Debian | libssh | forky | 0.12.2-1 | fixed |
| Debian | libssh | trixie | 0.11.5-0+deb13u1 | fixed |
| Debian | libssh | trixie-security | 0.11.5-0+deb13u1 | fixed |
| Debian | libssh | bookworm | 0.10.6-0+deb12u2 | fixed |
| Debian | libssh | bookworm-security | 0.10.6-0+deb12u3 | fixed |
| Ubuntu | libssh | 20.04 | 0.9.0-1ubuntu1 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.0-1ubuntu4 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.0-1ubuntu5 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu1 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu2 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu2.1 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu2.2 | fixed |
| Ubuntu | libssh | 22.04 | 0.9.6-1 | fixed |
| Ubuntu | libssh | 20.04 | 0.9.0-1ubuntu1 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.0-1ubuntu4 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.0-1ubuntu5 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu1 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu2 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu2.1 | vulnerable |
| Ubuntu | libssh | 20.04 | 0.9.3-2ubuntu2.2 | fixed |
Fixed-version evidence
| Distribution | Package | Type | Release | Fixed version | Urgency | Origin | Bugs |
|---|---|---|---|---|---|---|---|
| Debian | libssh | source | sid | 0.9.6-1 | not yet assigned | Not reported | [993046] |
| Debian | libssh | source | forky | 0.9.6-1 | not yet assigned | Not reported | [993046] |
| Debian | libssh | source | trixie | 0.9.6-1 | not yet assigned | Not reported | [993046] |
| Debian | libssh | source | bookworm | 0.9.6-1 | not yet assigned | Not reported | [993046] |
| Ubuntu | libssh | deb | 20.04 | 0.9.3-2ubuntu2.2 | Not reported | UBUNTU-CVE-2021-3634 | Not reported |
| Ubuntu | libssh | deb | 22.04 | 0.9.6-1 | Not reported | UBUNTU-CVE-2021-3634 | Not reported |
| Ubuntu | libssh | deb | 20.04 | 0.9.3-2ubuntu2.2 | Not reported | USN-5053-1 | Not reported |
OpenFactory catalog packages
Matching against OpenFactory catalog package versions is in progress.
[Debian 12 (Bookworm)]
- [libssh-4]Unknown
Source package: [libssh]
Details (4)
0.10.6-0+deb12u2· amd64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u2· arm64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· amd64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· arm64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
- [libssh-dev]Unknown
Source package: [libssh]
Details (4)
0.10.6-0+deb12u2· amd64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u2· arm64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· amd64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· arm64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
- [libssh-doc]Unknown
Source package: [libssh]
Details (4)
0.10.6-0+deb12u2· all · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u2· all · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· all · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· all · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
- [libssh-gcrypt-4]Unknown
Source package: [libssh]
Details (4)
0.10.6-0+deb12u2· amd64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u2· arm64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· amd64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· arm64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
- [libssh-gcrypt-dev]Unknown
Source package: [libssh]
Details (4)
0.10.6-0+deb12u2· amd64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u2· arm64 · bookwormFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· amd64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
0.10.6-0+deb12u1· arm64 · bookworm-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · bookworm; dsa · libssh · debian · 12
[Debian 13 (Trixie)]
- [libssh-4]Unknown
Source package: [libssh]
Details (4)
0.11.2-1+deb13u1· amd64 · trixieFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.2-1+deb13u1· arm64 · trixieFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.5-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.5-0+deb13u1· arm64 · trixie-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
- [libssh-dev]Unknown
Source package: [libssh]
Details (4)
0.11.2-1+deb13u1· amd64 · trixieFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.2-1+deb13u1· arm64 · trixieFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.5-0+deb13u1· amd64 · trixie-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.5-0+deb13u1· arm64 · trixie-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
- [libssh-doc]Unknown
Source package: [libssh]
Details (4)
0.11.2-1+deb13u1· all · trixieFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.2-1+deb13u1· all · trixieFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.5-0+deb13u1· all · trixie-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
0.11.5-0+deb13u1· all · trixie-securityFixed · Fixed:
0.9.6-1dsa · libssh · debian · 13
Observed:
References
- [https://access.redhat.com/errata/RHSA-2022:2031]
- [https://ftp.suse.com/pub/projects/security/csaf/rhsa-2022_2031.json]
- [https://osv.dev/vulnerability/DEBIAN-CVE-2021-3634]
- [https://osv.dev/vulnerability/DSA-4965-1]
- [https://osv.dev/vulnerability/UBUNTU-CVE-2021-3634]
- [https://osv.dev/vulnerability/USN-5053-1]
- [https://security-tracker.debian.org/tracker/CVE-2021-3634]
- [https://wid.cert-bund.de/.well-known/csaf/white/2021/wid-sec-w-2022-0001.json]
[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX]