CVE-2026-97560 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix one-byte OOB read in smb2_parse_native_symlink()
When parsing a share-root relative native symlink, memcpy copies smb_target+1 (skipping the leading separator) but uses strlen(smb_target)+1 as the length, reading one byte past the allocated buffer.
This fixes the following KASAN splat when accessing an SMB symlink with a target of '\a\b':
BUG: KASAN: slab-out-of-bounds in smb2_parse_native_symlink+0x4f5/0xca0 Read of size 5 at addr ffff88800878fe21 by task netfsfuzz-execu/1 CPU: 1 UID: 0 PID: 1 Comm: netfsfuzz-execu Tainted: G N 7.2.0-11943-g2709dd5ae32f-dirty #1 PREEMPT(lazy) Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996) Call Trace: <TASK> dump_stack_lvl+0x7b/0xa0 print_report+0xd0/0x630 kasan_report+0xe5/0x120 kasan_check_range+0x105/0x1b0 __asan_memcpy+0x23/0x60 smb2_parse_native_symlink+0x4f5/0xca0 parse_reparse_point+0x68a/0x1530 reparse_info_to_fattr+0x752/0xa20 cifs_get_fattr+0x873/0x15b0 cifs_get_inode_info+0xc0/0x310 cifs_lookup+0x308/0xa70 __lookup_slow+0x122/0x2b0 lookup_slow+0x50/0x70 path_lookupat+0x525/0xaf0 filename_lookup+0x1f2/0x550 vfs_statx+0xd1/0x1a0 vfs_fstatat+0x65/0xc0 __do_sys_newfstatat+0x9a/0x120 do_syscall_64+0xdd/0x4a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel SMB client implementation contains a critical memory safety vulnerability within the smb2_parse_native_symlink function, specifically affecting the parsing of share-root relative native symbolic links. This flaw manifests as an out-of-bounds read that occurs when processing specially crafted SMB symlink targets. The issue stems from a miscalculation in buffer length during string copying operations. When the parser encounters a target path beginning with a separator character indicating a share-relative reference, it attempts to skip this leading delimiter by advancing the source pointer by one byte. However, the subsequent memory copy operation utilizes strlen(smb_target)+1 as the total number of bytes to read from the adjusted buffer position. This logic fails to account for the fact that skipping the first character reduces the available data in the remaining portion of the string by exactly one byte relative to the original length calculation. Consequently, the memcpy function reads one byte past the end of the allocated memory region associated with smb_target.
This vulnerability is classified under CWE-125, which describes an out-of-bounds read error where software reads data beyond the intended boundary of a buffer. In the context of kernel development, such errors are particularly severe because they can lead to information disclosure or system instability depending on what memory contents reside at the adjacent location. The vulnerability was identified and triggered by KASAN (Kernel Address Sanitizer), which detected an invalid read operation within smb2_parse_native_symlink. The specific trigger involves a symlink target containing characters that result in a length calculation mismatch, such as targets starting with control characters like backspace or bell. The operational impact includes potential leakage of kernel memory contents to user space if the out-of-bounds data is subsequently processed and returned through file attribute retrieval mechanisms.
The attack vector for this vulnerability involves an attacker controlling the content of SMB symbolic links on a server accessible by the vulnerable client system. By creating symlinks with specific target paths that exploit the off-by-one error, an adversary can induce the kernel to perform unauthorized memory reads. While immediate exploitation leading to arbitrary code execution is less likely due to the read-only nature of this flaw, it significantly expands the attack surface for information disclosure attacks. The vulnerability affects systems running Linux kernels where the CIFS/SMB client module is active and configured to resolve native symlinks from remote shares. This includes common distributions that utilize the cifs filesystem driver for mounting SMB network shares.
Mitigation strategies primarily involve applying the upstream kernel patch that corrects the length calculation in smb2_parse_native_symlink. System administrators should ensure their systems are updated with the latest stable kernel versions provided by their distribution vendors, as these updates typically include fixes for recently disclosed vulnerabilities of this nature. For environments where immediate patching is not feasible, network-level controls such as firewalls can be configured to restrict SMB traffic from untrusted or potentially malicious servers. Additionally, disabling native symlink resolution in client configurations may reduce exposure if the feature is not strictly required by organizational workflows. Monitoring system logs for KASAN reports or unusual kernel oops messages can also aid in detecting potential exploitation attempts before they cause significant harm.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK technique T1083, which involves file and directory discovery, as the out-of-bounds read could potentially reveal sensitive system information that aids further reconnaissance. It also relates to CWE-200, an exposure of sensitive information to an unauthorized actor, due to the potential for kernel memory leakage. The fix ensures that the length parameter passed to memcpy accurately reflects the remaining valid data after skipping the separator character, thereby preventing access to uninitialized or unrelated memory regions. This correction reinforces the importance of rigorous bounds checking in low-level string manipulation routines within network protocol parsers, where malformed inputs from remote sources are a constant threat vector.