CVE-2025-21653 is a vulnerability identified in the Linux kernel, specifically related to the validation of the TCA_FLOW_RSHIFT attribute. This vulnerability allows an attacker to exploit the lack of validation, potentially leading to undefined behavior when shifting a 32-bit integer with large values. As indicated by the error message, a right shift of 9445 exceeds the limits of the 32-bit type 'u32', resulting in a shift-out-of-bounds condition.
The severity of this vulnerability is classified as medium with a CVSS score of 5.5. This classification signifies that while the impact is not critical, it still poses a significant risk to systems utilizing the affected versions of the Linux kernel. The risk to organizations includes potential disruptions in system availability, as the attack complexity is low, and the privileges required are also low.
At this time, there is no public exploit confirmed for this vulnerability, and it is not listed in the Known Exploited Vulnerabilities (KEV) catalog. However, organizations are encouraged to address this vulnerability promptly within their patch management processes, as the potential for exploitation exists.
Organizations should prioritize patching immediately, especially for those running affected versions of the Linux kernel, as unresolved vulnerabilities can lead to security breaches and operational disruptions.
Vulnerability Details
The vulnerability is rooted in the validation process of the TCA_FLOW_RSHIFT attribute in the Linux kernel's networking subsystem. The failure to validate this attribute can lead to unexpected behaviors during operations that involve shifting integers, which is particularly problematic when large shift values are employed. The vulnerability has been documented in the source code, with specific references to the file net/sched/cls_flow.c. The error highlighted by UBSAN indicates out-of-bounds shifting, which can compromise system stability.
The CVSS score of 5.5, categorized under the medium severity level, reflects the potential for high availability impact while indicating that confidentiality and integrity are not significantly affected. The attack vector is local, and while user interaction is not required, the complexity remains low, making it relatively easier for an attacker to exploit this vulnerability if left unaddressed.
The vulnerability affects multiple versions of the Linux kernel, specifically those ranging from version 2.6.25 to 6.12.10, as well as release candidates for version 6.13. Organizations must identify the specific versions in use and ensure timely updates.
Technical Analysis
The root cause of CVE-2025-21653 lies in the insufficient validation of input for the TCA_FLOW_RSHIFT attribute within the Linux kernel's networking code. When a user or a process attempts to shift a 32-bit integer by a large exponent, it can lead to a condition where the shift operation goes beyond the defined limits of the data type, resulting in undefined behavior. The attack vector for this vulnerability is local, meaning that an attacker must have access to the system to exploit it.
The attack complexity is considered low, as it does not require elevated privileges or user interaction. An attacker with low privileges can trigger this vulnerability under specific conditions. The potential impacts of this vulnerability include high availability impact, as the system may become unresponsive or crash due to the out-of-bounds operation. Confidentiality and integrity impacts are rated as none, indicating that this vulnerability does not lead to unauthorized data access or modification.
Risk & Impact Analysis
Risk to organizations includes potential service disruptions due to system crashes or unresponsiveness resulting from the exploitation of this vulnerability. The blast radius could be significant, particularly for organizations utilizing the affected versions of the Linux kernel across critical infrastructure and applications. Given that the attack complexity is low and the privileges required are also low, organizations must address this vulnerability in their patch management strategy.
The urgency assessment based on the CVSS score indicates that while the severity is medium, it is imperative for organizations to incorporate this into their priority patch cycle. The potential for disruption is a concern that cannot be overlooked, especially in production environments.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The following versions of the Linux kernel are affected by CVE-2025-21653: All versions from 2.6.25 up to, but not including, 5.4.290. Additionally, versions from 5.5 to 5.10.234, 5.11 to 5.15.177, and 5.16 to 6.1.125 are also vulnerable. Furthermore, versions 6.13:rc1 through 6.13:rc6 are susceptible. Organizations should ensure that they are running patched versions to mitigate this risk.
Mitigation & Remediation
Organizations should apply the latest patches provided by the Linux maintainers to remediate this vulnerability. Specific patches can be found in the following references: penetration testing services can also help identify any remaining vulnerabilities.
Detection Guidance
To detect potential exploitation of this vulnerability, organizations should monitor for log indicators associated with abnormal behavior during network operations. Behavioral anomalies, such as unexpected crashes or unresponsive states in network services, should be investigated promptly. Additionally, network signatures related to the TCA_FLOW_RSHIFT attribute may provide insights into attempted exploitations.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-21653 highlights the need for robust input validation mechanisms in the Linux kernel and similar systems. This vulnerability represents a pattern where insufficient validation can lead to critical failures, underscoring the importance of proactive security measures. Security teams should take this incident as a lesson to enhance their validation processes and ensure comprehensive testing of input handling in networking components.
Organizations are encouraged to adopt a continuous security posture by incorporating routine code reviews and vulnerability assessments into their development cycles. For further guidance on effective practices, security teams can refer to resources on penetration testing methodology and vulnerability management programs to strengthen their defenses.
Overall, CVE-2025-21653 serves as a critical reminder of the importance of rigorous input validation and the need for continuous monitoring to mitigate risks associated with vulnerabilities in foundational software like the Linux kernel.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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