CVE-2026-45933
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Heap-based Out-of-Bounds Write in Linux Kernel BPF

Publication date: 2026-05-27

Last updated on: 2026-05-30

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: bpf: Preserve id of register in sync_linked_regs() sync_linked_regs() copies the id of known_reg to reg when propagating bounds of known_reg to reg using the off of known_reg, but when known_reg was linked to reg like: known_reg = reg ; both known_reg and reg get same id known_reg += 4 ; known_reg gets off = 4, and its id gets BPF_ADD_CONST now when a call to sync_linked_regs() happens, let's say with the following: if known_reg >= 10 goto pc+2 known_reg's new bounds are propagated to reg but now reg gets BPF_ADD_CONST from the copy. This means if another link to reg is created like: another_reg = reg ; another_reg should get the id of reg but assign_scalar_id_before_mov() sees BPF_ADD_CONST on reg and assigns a new id to it. As reg has a new id now, known_reg's link to reg is broken. If we find new bounds for known_reg, they will not be propagated to reg. This can be seen in the selftest added in the next commit: 0: (85) call bpf_get_prandom_u32#7 ; R0=scalar() 1: (57) r0 &= 255 ; R0=scalar(smin=smin32=0,smax=umax=smax32=umax32=255,var_off=(0x0; 0xff)) 2: (bf) r1 = r0 ; R0=scalar(id=1,smin=smin32=0,smax=umax=smax32=umax32=255,var_off=(0x0; 0xff)) R1=scalar(id=1,smin=smin32=0,smax=umax=smax32=umax32=255,var_off=(0x0; 0xff)) 3: (07) r1 += 4 ; R1=scalar(id=1+4,smin=umin=smin32=umin32=4,smax=umax=smax32=umax32=259,var_off=(0x0; 0x1ff)) 4: (a5) if r1 < 0xa goto pc+4 ; R1=scalar(id=1+4,smin=umin=smin32=umin32=10,smax=umax=smax32=umax32=259,var_off=(0x0; 0x1ff)) 5: (bf) r2 = r0 ; R0=scalar(id=2,smin=umin=smin32=umin32=6,smax=umax=smax32=umax32=255) R2=scalar(id=2,smin=umin=smin32=umin32=6,smax=umax=smax32=umax32=255) 6: (a5) if r1 < 0xe goto pc+2 ; R1=scalar(id=1+4,smin=umin=smin32=umin32=14,smax=umax=smax32=umax32=259,var_off=(0x0; 0x1ff)) 7: (35) if r0 >= 0xa goto pc+1 ; R0=scalar(id=2,smin=umin=smin32=umin32=6,smax=umax=smax32=umax32=9,var_off=(0x0; 0xf)) 8: (37) r0 /= 0 div by zero When 4 is verified, r1's bounds are propagated to r0 but r0 also gets BPF_ADD_CONST (bug). When 5 is verified, r0 gets a new id (2) and its link with r1 is broken. After 6 we know r1 has bounds [14, 259] and therefore r0 should have bounds [10, 255], therefore the branch at 7 is always taken. But because r0's id was changed to 2, r1's new bounds are not propagated to r0. The verifier still thinks r0 has bounds [6, 255] before 7 and execution can reach div by zero. Fix this by preserving id in sync_linked_regs() like off and subreg_def.
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Meta Information
Published
2026-05-27
Last Modified
2026-05-30
Generated
2026-06-16
AI Q&A
2026-05-27
EPSS Evaluated
2026-06-15
NVD
CVE-2026-45933
EUVD
EUVD-2026-32217
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux_kernel linux_kernel *
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Exploitability
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability exists in the Linux kernel's BPF verifier, specifically in the function sync_linked_regs(). The issue arises when the function copies the id of a known register (known_reg) to another register (reg) while propagating bounds. If known_reg is linked to reg and then modified with an offset, reg incorrectly inherits a BPF_ADD_CONST id. When another register is linked to reg, the new id assignment breaks the link between known_reg and reg. As a result, updated bounds for known_reg are not propagated to reg, causing the verifier to have incorrect assumptions about register bounds.

This flaw can lead to incorrect verification of bounds in BPF programs, potentially allowing unsafe operations such as division by zero, which is demonstrated in the provided selftest example.

Impact Analysis

This vulnerability can impact you by causing the Linux kernel's BPF verifier to incorrectly validate BPF programs. Specifically, it can lead to unsafe conditions like division by zero due to improper propagation of register bounds.

Such incorrect verification may allow malicious or buggy BPF programs to execute operations that could cause kernel crashes or undefined behavior, potentially leading to denial of service or other stability issues in the system.

Mitigation Strategies

This vulnerability has been resolved in the Linux kernel by preserving the id of registers in the sync_linked_regs() function. To mitigate this vulnerability, you should update your Linux kernel to a version that includes this fix.

  • Identify your current Linux kernel version.
  • Check for available kernel updates from your distribution that include the fix for this vulnerability.
  • Apply the kernel update and reboot your system to load the patched kernel.
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