libssh2 up to 1.11.1 SSH src/sftp.c sftp_symlink link_len out-of-bounds

Summaryinfo

A vulnerability has been found in libssh2 up to 1.11.1 and classified as critical. This issue affects the function sftp_symlink of the file src/sftp.c of the component SSH Handler. This manipulation of the argument link_len causes out-of-bounds. This vulnerability is tracked as CVE-2025-15661. The attack is possible to be carried out remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical was found in libssh2 up to 1.11.1. Affected by this vulnerability is the function sftp_symlink of the file src/sftp.c of the component SSH Handler. The manipulation of the argument link_len with an unknown input leads to a out-of-bounds vulnerability. The CWE definition for the vulnerability is CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

libssh2 through 1.11.1, fixed in commit 2dae302, contains an out-of-bounds heap read vulnerability in the sftp_symlink() function in src/sftp.c that allows a malicious SSH server or man-in-the-middle attacker to disclose heap memory contents or cause a crash by sending a crafted SSH_FXP_NAME response. Attackers can supply a link_len value larger than the actual packet data in SSH_FXP_NAME responses for SFTP READLINK and REALPATH operations, triggering a heap buffer over-read of up to target_len minus one bytes due to the missing validation of available packet buffer size before the memcpy operation.

The weakness was disclosed by Joshua Rogers. The advisory is shared at github.com. This vulnerability is known as CVE-2025-15661 since 06/18/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available.

Upgrading eliminates this vulnerability. Applying the patch 2dae3024897e1898d389835151f4e9606227721d is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-2007). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Open Source libssh2

Productinfo

Name

• libssh2

Version

• 1.11.0
• 1.11.1

License

• open-source

Website

• Product: https://github.com/libssh2/libssh2/

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CPE 2.2info

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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