Linux Kernel up to 7.2.5 uprobes is_prefix_bad stack-based overflow

Summaryinfo

A vulnerability labeled as very critical has been found in Linux Kernel up to 7.2.5. This issue affects the function is_prefix_bad of the component uprobes. Executing a manipulation can lead to stack-based overflow. This vulnerability appears as CVE-2026-93164. The attack requires local access. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.2.5. It has been declared as very critical. This vulnerability affects the function is_prefix_bad of the component uprobes. The manipulation with an unknown input leads to a stack-based overflow vulnerability. The CWE definition for the vulnerability is CWE-121. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function). As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: uprobes/x86: Move optimized uprobe from nop5 to nop10 Andrii reported an issue with optimized uprobes [1] that can clobber redzone area with call instruction storing return address on stack where user code may keep temporary data without adjusting rsp. Fixing this by moving the optimized uprobes on top of 10-bytes nop instruction, so we can squeeze another instruction to escape the redzone area before doing the call, like: lea -0x80(%rsp), %rsp call tramp Note the lea instruction is used to adjust the rsp register without changing the flags. We use nop10 and following transformation to optimized instructions above and back as suggested by Peterz [2]. Optimize path (int3_update_optimize): 1) Initial state after set_swbp() installed the uprobe: cc 2e 0f 1f 84 00 00 00 00 00 From offset 0 this is INT3 followed by the tail of the original 10-byte NOP. After a previous unoptimization bytes 5..9 may still contain the old call instruction, which remains valid for threads already there. 2) Rewrite the LEA tail and call displacement: cc [8d 64 24 80 e8 d0 d1 d2 d3] From offset 0 this traps on the uprobe INT3. Bytes 1..9 are not executable entry points while byte 0 is trapped. 3) Publish the first LEA byte: [48] 8d 64 24 80 e8 d0 d1 d2 d3 From offset 0 this is: lea -0x80(%rsp), %rsp call <uprobe-trampoline> Unoptimize path (int3_update_unoptimize): 1) Initial optimized state: 48 8d 64 24 80 e8 d0 d1 d2 d3 Same as 3) above. 2) Trap new entries before restoring the NOP bytes: [cc] 8d 64 24 80 e8 d0 d1 d2 d3 From offset 0 this traps. A thread that had already executed the LEA can still reach the intact CALL at offset 5. 3) Restore bytes 1..4 of the original NOP while keeping byte 0 trapped and byte 5 as CALL. cc [2e 0f 1f 84] e8 d0 d1 d2 d3 From offset 0 this still traps. Offset 5 is still the CALL for any thread that was already past the first LEA byte. 4) Publish the first byte of the original NOP: [66] 2e 0f 1f 84 e8 d0 d1 d2 d3 From offset 0 this is the restored 10-byte NOP; the CALL opcode and displacement are now only NOP operands. Offset 5 still decodes as CALL for a thread that was already there. Tthere is only a single target uprobe-trampoline for the given nop10 instruction address, so the CALL instruction will not be changed across unoptimization/optimization cycles. Therefore, any task that is preempted at the CALL instruction is guaranteed to observe that CALL and not anything else. Note as explained in [2] we need to use following nop10: PF1 PF2 ESC NOPL MOD SIB DISP32 NOP10: 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 -- cs nopw 0x00000000(%rax,%rax,1) which means we need to allow 0x2e prefix which maps to INAT_PFX_CS attribute in is_prefix_bad function. Also changing the uprobe syscall error when called out of uprobe trampoline to -EPROTO, so we are able to detect the fixed kernel. The optimized uprobe performance stays the same: uprobe-nop : 3.129 ± 0.013M/s uprobe-push : 3.045 ± 0.006M/s uprobe-ret : 1.095 ± 0.004M/s --> uprobe-nop10 : 7.170 ± 0.020M/s uretprobe-nop : 2.143 ± 0.021M/s uretprobe-push : 2.090 ± 0.000M/s uretprobe-ret : 0.942 ± 0.000M/s --> uretprobe-nop10: 3.381 ± 0.003M/s usdt-nop : 3.245 ± 0.004M/s --> usdt-nop10 : 7.256 ± 0.023M/s [1] https://lore.kernel.org/bpf/[email protected]/ [2] https://lore.kernel.org/bpf/[email protected]/#t

The advisory is available at git.kernel.org. This vulnerability was named CVE-2026-93164 since 09/17/2026. The exploitation appears to be easy. Local access is required to approach this attack. Additional levels of successful authentication are necessary for exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 09/17/2026).

Upgrading to version 7.2.6 or 7.3-rc1 eliminates this vulnerability. Applying the patch 1b3fecd09910040668b752f3377d7218ca5c59ac/554ba38456dad8053a1a80afe6ae6da9eff745cc is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5

License

• open-source

Website

• Vendor: https://www.kernel.org/

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