CVE-2026-52967: Linux Kernel SMB Client Infinite Loop and Memory Read Vulnerability

Technical summary

CVE-2026-52967 is a boundary-checking defect in the kernel's `symlink_data()` function within the SMB/CIFS client implementation. The flaw occurs when an `ErrorDataLength` field in an SMB response is set to specific large values (0xfffffff8 or 0xfffffff0). On 32-bit architectures, pointer arithmetic with these values causes either a wraparound that points back to the structure itself (infinite loop scenario) or a negative offset that accesses memory before the structure (out-of-bounds read). The calculation `u8 *next = p->ErrorContextData + len` lacks proper validation to ensure the resulting pointer remains within allocated boundaries.

Business impact

Exploiting this vulnerability could lead to denial of service through system hangs, or information disclosure if an attacker can leak kernel memory contents. For organizations relying on SMB/CIFS mounts to network storage or domain authentication, a compromise could disrupt file access or expose sensitive credentials cached in kernel memory. The attack surface includes any system configured to mount remote SMB shares, particularly in enterprise environments with centralized file servers or Active Directory integration.

Affected systems

The Linux kernel across all supported versions prior to patching. Exposure is highest on 32-bit architectures due to the pointer arithmetic behavior, but the code path exists in 64-bit kernels as well. Any distribution shipping the vulnerable kernel code is affected, including enterprise variants (RHEL, SLES, Ubuntu LTS) and community distributions. Systems with SMB client functionality enabled and that connect to SMB shares are at risk; disconnected systems or those without SMB/CIFS modules loaded have reduced exposure.

Exploitability

Exploitation requires user interaction (a user or automated system must initiate an SMB connection to an attacker-controlled or compromised SMB server). No authentication is required on the SMB side; the attacker simply responds with a crafted error response containing a malicious ErrorDataLength value. The vulnerability is reliably triggered—once the pointer arithmetic occurs, the outcome is deterministic. However, the need for an active SMB connection and the requirement for the victim's kernel to contain the vulnerable code path limits widespread automated exploitation.

Remediation

Apply kernel updates that include the fix to the `symb olic_data()` function. The patch validates ErrorDataLength values before using them in pointer arithmetic, likely by checking against the structure size or response buffer length. Verify availability of patched kernel versions from your distribution vendor. In the interim, restrict SMB connections to trusted servers and monitor SMB client traffic for suspicious patterns. Disabling SMB client functionality entirely is impractical for most enterprises but may be considered in high-security environments that do not require SMB access.

Patch guidance

Kernel patches addressing this issue should be available through your Linux distribution's package manager (apt, yum, zypper, etc.). Update priorities should align with your organization's patch cadence; given the requirement for user interaction and the HIGH severity, treat this as a standard-priority patch for most environments, with accelerated timelines for high-value targets. After patching, test SMB mount functionality to ensure no regressions. Monitor distribution security advisories for the specific CVE to confirm patch inclusion and any prerequisites.

Detection guidance

Intrusion detection can focus on SMB protocol anomalies: look for SMB error responses with unusually large ErrorDataLength fields (especially values near 0xffffffff) sent to internal hosts. Kernel logs may show oops, page faults, or hang signatures correlated with SMB client activity. Host-based detection is challenging since the flaw is exploited during normal SMB protocol handling; focus on network-level detection of malformed SMB responses. Monitor for system hangs or unresponsive processes on hosts actively mounting SMB shares, and correlate with SMB connection attempts during the same window.

Why prioritize this

Despite the HIGH CVSS score and potential for information disclosure, the requirement for user/administrator interaction to connect to a malicious or compromised SMB server, combined with the lack of CISA KEV listing, suggests this is not an immediate, widespread exploit-in-the-wild threat. However, it merits prioritized patching because: (1) SMB is common in enterprise networks, (2) kernel vulnerabilities are attractive targets, (3) memory disclosure can compromise credentials, and (4) DoS through system hang impacts availability. Prioritize patching for systems that actively mount SMB shares, especially domain-joined machines.

Risk score, explained

The CVSS 3.1 score of 8.1 (HIGH) reflects high impact (confidentiality and availability) with a low complexity attack vector requiring no privileges, balanced by the requirement for user interaction (UI:R) and user-scoped impact. The score appropriately captures the seriousness of a kernel memory leak or hang, but in real-world context, the exploitation barrier (needing an active SMB connection to an attacker-controlled server) is higher than the CVSS model weights. Treat the score as a guide, not a ceiling; risk in your environment depends on SMB usage patterns and trust boundaries.

Frequently asked questions