CVE-2026-89630

A flaw was found in the Linux kernel's Server Message Block (SMB) client. An incorrect calculation of the data_offset bound in the is_valid_oplock_break() function can lead to a read overflow. This vulnerability allows a malicious SMB server to potentially trigger an out-of-bounds read, which could result in information disclosure or a denial of service.

An out of bounds read in the SMB client oplock break validation path can occur because is_valid_oplock_break uses an ineffective DataOffset bound after the RFC1002 preamble accounting changed. A malicious or compromised SMB server can send a crafted SMB1 notification or oplock related response with an invalid DataOffset, causing the Linux client kernel to read beyond the received SMB message and potentially crash. For the CVSS the PR:N because the attacker does not need privileges on the victim and only needs control of or ability to impersonate an SMB server that the client communicates with. UI:R is used because the client normally has to mount or connect to the malicious server or an already configured share must point to a compromised endpoint. The issue is network reachable from server to client. Impact is at least denial of service via kernel crash, with limited confidentiality impact considered only in the paranoid score due to the out of bounds read primitive.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.