Cyber Resilience

CVE-2026-66032

Memory Safety in Libssh2 ≤ 1.11.1

Public PoCMemory Safety
Published
24 July 2026
Modified
07 August 2026
Patch / advisory
View advisory
CVSS Score v4 8.7
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0028 20th percentile
Risk Priority 55 floored blend · peak EPSS

Summary

CVE-2026-66032 is a high-severity Double Free (CWE-415) vulnerability in Libssh2 Libssh2. Its CVSS base score is 8.7 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked at the 20th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-8 (Security and Privacy Engineering Principles) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)
CWE-415

Related Threats

MITRE ATT&CK Enterprise Techniques

T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
T1499 Endpoint Denial of Service Impact
Adversaries may perform Endpoint Denial of Service (DoS) attacks to degrade or block the availability of services to users.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-66035Same product: Libssh2 Libssh2
CVE-2026-55200Same product: Libssh2 Libssh2
CVE-2025-15661Same product: Libssh2 Libssh2
CVE-2026-66033Same product: Libssh2 Libssh2
CVE-2026-7598Same product: Libssh2 Libssh2
CVE-2026-58050Same product: Libssh2 Libssh2
CVE-2026-66034Same product: Libssh2 Libssh2
CVE-2026-55199Same product: Libssh2 Libssh2
CVE-2026-58051Same product: Libssh2 Libssh2
CVE-2025-61990Shared CWE-415

Affected Assets

libssh2
libssh2
≤ 1.11.1

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 1 hardening rule · 1 OS baseline
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation explicitly includes dynamic analysis and fuzzing that locate double-free defects before release.

SA-8 Security and Privacy Engineering Principles partial match

Security engineering principles can require memory-safe allocation patterns or language features that structurally eliminate double-free opportunities.

SI-2 Flaw Remediation partial match

Flaw remediation processes require identification and correction of memory-management defects such as double free once discovered.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 full match
prevents

Secure SDLC practices directly prevent double-free errors via static analysis, safe memory APIs, and testing.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development can detect double-free conditions before release.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle includes memory-safety practices that can prevent double-free bugs.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate memory-safety rules that reduce double-free risk.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure system architecture and engineering principles can prescribe safe memory-management patterns.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly address proper use of free() and similar functions.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (1 rule)
  • V-248590 OL 8 must clear the page allocator to prevent use-after-free attacks. prevents CWE-415

References