Medium [CVE-2026-66032] Arbitrary code execution via double-free in SFTP session
This medium-severity Red Hat Linux advisory covers CVE-2026-66032 affecting Red Hat Enterprise Linux 7 Extended Lifecycle Support, Red Hat Hardened Images, Red Hat Enterprise Linux 6.
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Summary
libssh2 through 1.11.1, fixed in commit 5e47761, contains a double-free vulnerability in the sftp_open() function in src/sftp.c that allows a malicious SSH server to corrupt the heap of any authenticated client opening an SFTP session.
When a server responds to SSH_FXP_OPEN with SSH_FXP_STATUS containing FX_OK, the response data buffer is freed, and if a subsequent sftp_packet_require() call returns a specific error such as LIBSSH2_ERROR_CHANNEL_PACKET_EXCEEDED, the same pointer is freed a second time, enabling tcache dup conditions on glibc systems that allow overlapping allocations and function pointer overwrites.
A flaw was found in libssh2. This heap corruption can lead to arbitrary code execution on the client system, giving the attacker control over the affected system.
This flaw requires user interaction, as a client must connect to a specially crafted server and initiate an SFTP transfer, which can lead to arbitrary code execution on the client system. Red Hat severity: Moderate — CVSS 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H).
Weakness: CWE-1341. Affected Red Hat products: Red Hat Enterprise Linux 7 Extended Lifecycle Support; Red Hat Hardened Images; Red Hat Enterprise Linux 6.
Will not fix / out of support: Red Hat Enterprise Linux 6. Red Hat fixing advisory: RHSA-2026:61752, RHSA-2026:46927.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · high-confidence parse· fetched 27 days ago·verify at source
- 1.11.1
- libssh2-0:1.8.0-4.el7_9.2
- libssh2-main-1.11.1-10.2.hum1
- RHSA-2026:61752
- RHSA-2026:46927
Official advisory · high-confidence parse· fetched 27 days ago·verify at source
Mitigation checklist
- Restrict your libssh2 clients to connect only to fully trusted, internal SFTP servers to eliminate exposure to malicious server responses. Additionally, configure dependent applications with Restart=on-failure in systemd so RHEL's glibc memory protections can safely crash and auto-recover the process during an attack.
Official advisory · high-confidence parse· fetched 27 days ago·verify at source
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