Libssh
CVE-2021-3634
MEDIUM
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, write limits
MITRE ATT&CK
2 techniques across 2 tactics: Execution, Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 6.5 (MEDIUM). Attack characteristics: network attack vector, low complexity, low privileges required, no user interaction not required. |
| Exploit ScenarioDerived | A remote attacker could write data beyond allocated buffer boundaries leading to code execution or crashes by sending crafted requests to the affected application. |
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Alert meAnalysisAI
A flaw has been found in libssh in versions prior to 0.9.6. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. This Out-of-bounds Write vulnerability could allow attackers to write data beyond allocated buffer boundaries leading to code execution or crashes.
RemediationAI
A vendor patch is available. Apply the latest security update as soon as possible. Validate write boundaries, use memory-safe languages, enable compiler protections (ASLR, stack canaries).
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as Out-of-bounds Write (CWE-787), which allows attackers to write data beyond allocated buffer boundaries leading to code execution or crashes. 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. Affected products include: Libssh, Redhat Virtualization, Redhat Enterprise Linux, Debian Debian Linux, Fedoraproject Fedora. Version information: prior to 0.9.6..
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
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.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.
Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.
Affected Products (CPE)NVD
The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6 and other products, allows remot
A vulnerability was found in libssh's server-side state machine before versions 0.7.6 and 0.8.4. Rated critical severity
libssh 0.9.4 has a NULL pointer dereference in tftpserver.c if ssh_buffer_new returns NULL. Rated medium severity (CVSS
Multiple integer overflows in libssh before 0.5.3 allow remote attackers to cause a denial of service (infinite loop or
Multiple buffer overflows in libssh before 0.5.3 allow remote attackers to cause a denial of service (crash) or possibly
Cryptographic key derivation failure in libssh versions prior to 0.11.2 (when built against OpenSSL older than 3.0) can
A flaw was found with the libssh API function ssh_scp_new() in versions before 0.9.3 and before 0.8.8. Rated high severi
A flaw was found in libssh when using the ChaCha20 cipher with the OpenSSL library.
The (1) SSH_MSG_NEWKEYS and (2) SSH_MSG_KEXDH_REPLY packet handlers in package_cb.c in libssh before 0.6.5 do not proper
Double free vulnerability in the sftp_mkdir function in sftp.c in libssh before 0.5.3 allows remote attackers to cause a
Multiple double free vulnerabilities in the (1) agent_sign_data function in agent.c, (2) channel_request function in cha
Stack-based buffer overflow in libssh's SFTP server allows a connected client to crash the server or potentially execute
GitHub PoC
Exploit-DB