A newly discovered vulnerability in the Linux kernel’s Virtual Socket (vsock) implementation, tracked as CVE-2025-21756, has sent shockwaves through the cybersecurity community.
This flaw, which has received a CVSS v3.1 Base Score of 7.8 (High), allows local attackers to escalate privileges to root-potentially granting them full control over affected systems.
Technical Details
The vulnerability arises from improper handling of socket bindings during transport reassignment in the vsock subsystem.
Specifically, the kernel fails to correctly manage the reference counter for sockets, leading to a use-after-free (UAF) condition.
When a socket’s reference count is erroneously decremented, it can be freed while still accessible, opening the door for attackers to manipulate freed memory and execute arbitrary code.
Security researchers have demonstrated that this UAF can be reliably triggered on vulnerable systems, enabling attackers with local access to escalate their privileges.
The exploit involves creating and manipulating vsock sockets, triggering the UAF, and then reclaiming the freed memory with attacker-controlled data.
This allows for the corruption of critical kernel structures and, ultimately, the execution of code with root privileges.
Impact and Exploitation
The consequences of CVE-2025-21756 are severe:
- Privilege Escalation: Local users can gain root access, bypassing standard security controls.
- Denial of Service (DoS): Exploitation may crash the system or render it unresponsive, disrupting services and business operations.
- Data Corruption or Leakage: Attackers could manipulate or extract sensitive data, leading to potential breaches.
A public proof-of-concept (PoC) exploit exists, increasing the urgency for organizations to patch affected systems immediately.
Affected Versions and Patch
The vulnerability affects Linux kernel versions before 6.6.79, 6.12.16, 6.13.4, and 6.14-rc1.
The Linux kernel maintainers have released a patch that introduces a check to ensure socket bindings are preserved until socket destruction, effectively mitigating the flaw.
Risk Factor Table
| Risk Factor | Details |
|---|---|
| Affected Products | Linux kernel with vsock (Virtual Socket) implementation (versions < 6.6.79, 6.12.16, 6.13.4, 6.14-rc1) |
| Impact | Privilege escalation to root possible |
| Exploit Prerequisites | Local access with the ability to create/manipulate vsock sockets; low complexity; no user interaction required; attacker must have local privilege |
| CVSS 3.1 Score | 7.8 (High) |
Urgent Recommendations
Security experts strongly advise all organizations and users running affected Linux versions to apply the latest security updates without delay.
The presence of a public exploit and the high impact of successful attacks make this vulnerability a critical risk for any unpatched system.
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