SB20260831114 - Ubuntu update for libssh
Published: August 31, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 9 vulnerabilities.
1) Stack-based buffer overflow (CVE-ID: CVE-2026-15370)
CWE-ID: CWE-121 - Stack-based buffer overflow
CVSSv4: 7.1 [CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a local user to execute arbitrary code.
The vulnerability exists due to stack-based buffer overflow in the sftp server longname field construction when listing an attacker-controlled directory with long filenames. A local user can cause a user to list a crafted directory to execute arbitrary code.
User interaction is required to list files in an attacker-controlled directory on a filesystem that allows long filenames.
2) Infinite loop (CVE-ID: CVE-2026-59843)
CWE-ID: CWE-835 - Loop with Unreachable Exit Condition ('Infinite Loop')
CVSSv4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to an infinite loop in channel_write_common() when processing an SSH_MSG_CHANNEL_OPEN request with a maximum packet length of zero. A remote user can send a specially crafted channel open request to cause a denial of service.
Repeating the attack over multiple connections can exhaust CPU resources of the server.
3) Input validation error (CVE-ID: CVE-2026-59844)
CWE-ID: CWE-20 - Improper input validation
CVSSv4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to improper input validation in the libssh SFTP server when processing SSH_FXP_READ requests. A remote user can send a specially crafted SSH_FXP_READ request with an excessive read length value to cause a denial of service.
The issue can be sustained by repeatedly issuing large read requests simultaneously over multiple SFTP channels.
4) Improper Check or Handling of Exceptional Conditions (CVE-ID: CVE-2026-59845)
CWE-ID: CWE-703 - Improper Check or Handling of Exceptional Conditions
CVSSv4: 6.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a local user to cause a denial of service.
The vulnerability exists due to improper handling of fork() failure in ProxyCommand execution in the libssh client when cleaning up a session after executing a ProxyCommand. A local user can trigger a fork() failure and then cause the process to send a KILL signal to process group -1 to cause a denial of service.
This issue affects the client only and typically occurs under low-memory conditions.
5) OS Command Injection (CVE-ID: CVE-2026-59846)
CWE-ID: CWE-78 - Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
CVSSv4: 4.6 [CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a local user to disclose sensitive information.
The vulnerability exists due to improper neutralization of special elements in the ProxyCommand username expansion in the client component when expanding a user-supplied username into a ProxyCommand executed by the shell. A local user can supply a malicious username and trick the victim into initiating a connection to disclose sensitive information.
User interaction is required to initiate the connection, and the issue is limited to the client side.
6) Improper validation of integrity check value (CVE-ID: CVE-2026-59847)
CWE-ID: CWE-354 - Improper Validation of Integrity Check Value
CVSSv4: 8.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to modify plaintext transmitted over the connection without being detected.
The vulnerability exists due to improper integrity check in the OpenSSL AES-GCM backend when processing encrypted SSH traffic. A remote attacker can flip bits in packets in transit to modify plaintext transmitted over the connection without being detected.
Only OpenSSL-based server and client configurations using the affected AES-GCM ciphers are vulnerable. Successful exploitation requires knowledge of the expected plaintext format of the packets.
7) Resource exhaustion (CVE-ID: CVE-2026-59848)
CWE-ID: CWE-400 - Resource exhaustion
CVSSv4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to improper handling of unexpected responses in the sftp client response queue when processing server-supplied sftp response packets. A remote attacker can send response packets with unknown request IDs to cause a denial of service.
The issue affects the client side only.
8) Always-Incorrect Control Flow Implementation (CVE-ID: CVE-2026-59849)
CWE-ID: CWE-670 - Always-Incorrect Control Flow Implementation
CVSSv4: 2.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to improper state management in ssh_userauth_publickey_auto() when handling automatic public key authentication with configured certificates. A remote user can reject a configured certificate or trigger error handling for a missing configured certificate to cause a denial of service.
Only the client side is affected, and exploitation requires a specific configuration in which certificate-based automatic authentication is used; the infinite loop occurs when the server does not enforce an authentication limit.
9) Use-after-free (CVE-ID: CVE-2026-59850)
CWE-ID: CWE-416 - Use After Free
CVSSv4: 5.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to use-after-free in channel data callbacks when processing data on closed channels. A remote user can send data through a closed channel to cause a denial of service.
The issue affects both server and client components and is exemplified on SFTP channels.
Remediation
Install update from vendor's website.