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Multiple vulnerabilities in libssh2 have exposed SSH clients and products that embed the library to attacks from malicious or impersonated SSH servers. The most severe issue, CVE-2026-55200, is a pre-authentication out-of-bounds heap write in ssh2_transport_read() that affects all versions through 1.11.1 and could allow remote code execution, while CVE-2026-55199 can force clients into a CPU-intensive loop during key exchange and cause denial of service. The library is widely used in curl, backup software, IoT firmware, and network appliances, raising broad supply-chain risk, especially where libssh2 is statically linked or bundled into downstream products.
A separate flaw, CVE-2025-15661, affects sftp_symlink() in src/sftp.c and can be triggered during SFTP READLINK or REALPATH operations when a malicious server or man-in-the-middle sends a crafted SSH_FXP_NAME response with an oversized link_len value. That bug causes a heap buffer over-read that may disclose memory contents or crash applications. Fixes were reported in commits 97acf3d, 1762685, and 2dae302, but at the time of reporting no official libssh2 release containing the newer patches had been published, leaving downstream vendors responsible for shipping their own updates.
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9 events from the most recent confirmed update back to the earliest known activity.
The Rust team released Rust 1.96.1, a point update that remediates three libssh2 vulnerabilities in the copy compiled into Cargo: CVE-2025-15661, CVE-2026-55199, and CVE-2026-55200. The release represents a downstream product update beyond the previously documented upstream libssh2 fixes and Debian advisory.
A Register report on the removed 'exploitarium' repository said the libssh2 flaw CVE-2026-55200 was already under active exploitation when the exploit code and write-up were published. This marks an escalation from earlier reporting that had not confirmed in-the-wild exploitation.
A new high-severity libssh2 vulnerability, CVE-2026-58050, was published describing an integer overflow in publickey subsystem attribute allocation affecting libssh2 through version 1.11.1. The flaw can let a malicious SSH server trigger an undersized heap allocation and out-of-bounds writes on 32-bit platforms during attribute parsing in a connecting client.
A GitHub repository published proof-of-concept exploits targeting the libssh2 publickey subsystem, including a Win32 integer-overflow allocation-wrap path and a Win64 stale-cleanup/arbitrary-free chain, with demonstrations that launch calc.exe. The repository also documented two hardening changes—zero-initializing grown list entries and rejecting overflowing num_attrs allocations—that reportedly blocked the demonstrated exploit paths.
Debian issued security advisory DSA-6365-1 for libssh2, indicating a downstream security update for the library. This adds a vendor response and package distribution milestone beyond the previously documented upstream fixes and disclosure.
A disclosure detailed CVE-2026-55200 and CVE-2026-55199 as affecting libssh2 through version 1.11.1, warning that the library's widespread use in tools, firmware, and appliances creates broad supply-chain exposure. At the time of the report, no official release containing the fixes had been published and no confirmed in-the-wild exploitation or public proof-of-concept was reported.
Fixes for two pre-authentication libssh2 vulnerabilities were merged into the master branch as commits 97acf3d and 1762685. The flaws are CVE-2026-55200, an out-of-bounds heap write in ssh2_transport_read() that could enable remote code execution, and CVE-2026-55199, a denial-of-service issue caused by insufficient validation during key exchange.
A GitHub repository published technical exploit details for CVE-2026-55200 in libssh2, describing the packet_length integer wraparound, undersized allocation, and resulting out-of-bounds write path in ssh2_transport_read(). The repository also included PoC components such as an arithmetic verifier, a malicious SSH server scaffold, and a controlled local RCE harness demonstrating callback overwrite and proof-file creation.
A heap buffer over-read in libssh2's sftp_symlink() function, tracked as CVE-2025-15661, was fixed in commit 2dae302. The flaw affects libssh2 through version 1.11.1 and can be triggered by a malicious SSH server or man-in-the-middle during SFTP READLINK or REALPATH operations.
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A high-severity memory-safety flaw tracked as **CVE-2026-66032** was disclosed in **libssh2** through version `1.11.1`, affecting the `sftp_open()` function in `src/sftp.c`. The bug allows a malicious SSH server to trigger a **double free** in an authenticated client that opens an SFTP session, creating heap corruption conditions. Advisory details say the issue occurs when the server responds to `SSH_FXP_OPEN` with `SSH_FXP_STATUS` containing `FX_OK` and a later `sftp_packet_require()` call returns a specific error such as `LIBSSH2_ERROR_CHANNEL_PACKET_EXCEEDED`, causing the same response buffer to be freed twice. The libssh2 project addressed the flaw in commit `5e4776146552d898b9c0e1b313cd093fa8dc92d0`, merged through pull request **#2180**, by nullifying the pointer after it is freed in the SFTP code. The fix, which also resolves advisory `GHSA-px3w-7g75-hg7w`, credits **VladimirEliTokarev** for reporting the issue. Security writeups warn that on glibc-based systems the bug can produce **tcache-dup** style heap corruption, potentially enabling overlapping allocations and function pointer overwrites, and users are advised to update libssh2 or apply the patch and recompile.
Jul 25, 2026
Libssh released versions **0.12.1** and **0.11.5** to fix multiple security issues, including **CVE-2026-59851**, an authentication bypass in deployments where `GSSAPIKeyExchange` is enabled on servers. The flaw allows an authenticated client to log in as an arbitrary local user because the `gssapi-keyex` path fails to verify whether the authenticated Kerberos principal is authorized for the requested account. The vulnerability is tracked as **CWE-863** and carries a **CVSS v3.1** score reflecting high impact to confidentiality, integrity, and availability. The **0.12.1** release addresses **11 CVEs**, while **0.11.5** backports fixes for **8 CVEs** affecting the 0.11 branch. In addition to the authentication bypass, the updates remediate a stack buffer overflow, information disclosure bugs, several denial-of-service conditions, a use-after-free issue, and an integrity downgrade flaw, alongside hardening changes such as zero-initializing `ssh_string` objects and validating peer public keys during Diffie-Hellman key exchange. Red Hat reported **RHEL 8** and **RHEL 9** as unaffected by `CVE-2026-59851`, listed **RHEL 10** status as unknown, and marked **Red Hat Hardened Images** as affected for `libssh` and `libssh2` package entries.
Jul 21, 2026
Two vulnerabilities in **sshfs** were disclosed and fixed in version **3.7.6**, affecting versions up to **3.7.5**. The more severe issue, **CVE-2026-47187**, is a symlink escape flaw that lets a rogue SFTP server trick the client into reading from or writing to unintended paths on the local filesystem by returning unsafe symlink targets. The second bug, **CVE-2026-48711**, is an argument injection weakness in hostname parsing that can turn a crafted mount source into an SSH option, enabling arbitrary local command execution under specific conditions and, in some cases, without requiring SSH authentication. Public technical details and exploit code have now been released, raising the risk of active abuse against systems that use sshfs to mount remote directories over SFTP. The flaws were privately reported by Abhinav Agarwal and addressed through a coordinated release, but defenders are being urged to upgrade immediately to **sshfs 3.7.6 or later** and verify trusted remote server keys, as a malicious or spoofed server could otherwise trigger client-side compromise.
Jun 29, 2026