kernel

Security Advisory

High-Severity Linux Kernel Flaw Exposes Systems to Root-Level Attacks

Security advisory: Linux Kernel Flaw raised from vulnerability related to improper memory handling when the splice() function is called. Specifically, the kTLS code fails to correctly update the internal accounting of the plaintext scatter-gather buffer, leading to an out-of-bounds memory write flaw. 

OEMLinux
SeverityHigh
CVSS Score7.8
CVEsCVE-2025-21756
POC AvailableYes
Actively ExploitedNo
Exploited in WildNo
Advisory Version1.0

Overview

A high-severity vulnerability (CVE-2025-21756) has been discovered in the Linux kernel’s Virtual Socket (vsock) implementation, allowing local privilege escalation to root via a use-after-free (UAF) condition caused by incorrect reference counting during socket binding operations.

Vulnerability NameCVE IDProduct AffectedSeverityCVSS Score
​ Use-After-Free vulnerability  CVE-2025-21756Linux kernel  High  7.8

Technical Summary

The kTLS subsystem in the Linux Kernel enables direct TLS encryption and authentication functions within the kernel, supporting secure communication for protocols like HTTPS, email, and other internet-connected applications.

CVE IDSystem AffectedVulnerability DetailsImpact
    CVE-2025-21756    Linux kernel (pre-6.6.79, 6.12.16, 6.13.4, and 6.14-rc1)Improper handling of reference counts in vsock_remove_sock() leads to premature freeing of vsock objects. Attackers can exploit the Use-After- Free (UAF) by reclaiming free memory using crafted pipe buffers and leveraging unprotected tools like vsock_diag_dump() to leak kernel pointers.      Local privilege escalation to root and potential full system compromise.

CVE-2025-21756 is a use-after-free vulnerability in the Linux kernel’s vsock subsystem. It arises due to incorrect reference counter management during transport reassignment of sockets, leading to memory corruption and potential privilege escalation.

Affected systems are particularly exposed in virtualized environments where vsock is actively used.

Remediation:

  • Update Linux Kernel: Users should update their systems immediately with the latest kernel versions
  • Restrict Local Access: Until patches are applied, limit vsock use in shared environments and restrict local access where feasible.
  • Monitor for Exploitation Attempts: Watch for anomalies related to the vsock subsystem, including unexpected kernel panics or vsock socket activity.
  • Review Security Module Configurations: While AppArmor and similar LSMs offer partial protection, ensure they are enabled and correctly configured.

Conclusion:
CVE-2025-21756 poses a significant threat to Linux systems, particularly in cloud and virtualized environments. Its discovery and detailed analysis by Michael Hoefler revealed not only a critical vulnerability but also advanced exploitation techniques capable of bypassing protections like AppArmor and KASLR.

Given the existence of public proof-of-concept code and reliable attack paths, organizations must prioritize patching and mitigation to avoid root-level compromise.

References:



Security Advisory

PoC Released for High-Severity Linux Kernel UVC Driver Vulnerability

OEMLinux
SeverityHIGH
CVSS7.8
CVEsCVE-2024-53104
Actively ExploitedYes
Publicly POC AvailableYes
Patch/Remediation AvailableYes
Advisory Version1.0

Overview

CVE-2024-53104 is a high-severity out-of-bounds write vulnerability in the Linux kernel’s USB Video Class (UVC) driver, leading to privilege escalation. The issue affects Linux kernel versions 2.6.26 and later. The vulnerability has gained renewed attention as a proof-of-concept (PoC) exploit has now been publicly released, increasing the risk of exploitation. A patch has been released to address this vulnerability, but unpatched systems remain at high risk.

Vulnerability NameCVE IDProduct AffectedSeverity
  out-of-bounds write vulnerability  CVE-2024-53104  Linux Kernel    High

Technical Summary

The vulnerability exists in the uvc_parse_format function of the UVC driver (uvc_driver.c). It arises due to improper parsing of UVC_VS_UNDEFINED frames, leading to incorrect buffer allocation and out-of-bounds writes.

An attacker could exploit this flaw by inserting a malicious USB device or manipulating video streams, potentially leading to memory corruption, privilege escalation, or arbitrary code execution.

CVE IDSystem AffectedVulnerability DetailsImpact
  CVE-2024-53104    Linux Kernel (2.6.26 and later)  Incorrect parsing of UVC_VS_UNDEFINED frames in uvc_parse_format, leading to miscalculated buffer sizes and memory corruption.    Privilege escalation, system instability, arbitrary code execution  

Remediation:

  • Apply Security Patches: Ensure that the latest security patches provided by the Linux distribution maintainers are promptly applied to mitigate vulnerability.

Recommendations

  • Implement USB Device Control Policies: Organizations should establish and enforce USB device control policies to prevent unauthorized usage and ensure only approved devices can be connected.
  • Deploy Log Monitoring and Analysis Tools: Implement security monitoring tools to continuously monitor logs for potential security incidents, such as exploitation attempts or suspicious activity.

Conclusion:

CVE-2024-53104 is a major vulnerability that poses a substantial risk to Linux systems since it allows for privilege escalation and arbitrary code execution. Users and administrators are strongly urged to apply the latest security patches to mitigate the risk of exploitation. Additionally, implementing a multi-layered security approach can further enhance system protection.

The Cybersecurity and Infrastructure Security Agency (CISA) has added this vulnerability to its Known Exploited Vulnerabilities (KEV) list, emphasizing the need for immediate remediation.

CISA has ordered federal agencies to secure their systems within three weeks against a high-severity Linux kernel flaw actively exploited in attacks.

References:

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