CVE-2024-41003: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2024-41003

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix reg_set_min_max corruption of fake_reg Juan reported that after doing some changes to buzzer [0] and implementing a new fuzzing strategy guided by coverage, they noticed the following in one of the probes: [...] 13: (79) r6 = *(u64 *)(r0 +0) ; R0=map_value(ks=4,vs=8) R6_w=scalar() 14: (b7) r0 = 0 ; R0_w=0 15: (b4) w0 = -1 ; R0_w=0xffffffff 16: (74) w0 >>= 1 ; R0_w=0x7fffffff 17: (5c) w6 &= w0 ; R0_w=0x7fffffff R6_w=scalar(smin=smin32=0,smax=umax=umax32=0x7fffffff,var_off=(0x0; 0x7fffffff)) 18: (44) w6 |= 2 ; R6_w=scalar(smin=umin=smin32=umin32=2,smax=umax=umax32=0x7fffffff,var_off=(0x2; 0x7ffffffd)) 19: (56) if w6 != 0x7ffffffd goto pc+1 REG INVARIANTS VIOLATION (true_reg2): range bounds violation u64=[0x7fffffff, 0x7ffffffd] s64=[0x7fffffff, 0x7ffffffd] u32=[0x7fffffff, 0x7ffffffd] s32=[0x7fffffff, 0x7ffffffd] var_off=(0x7fffffff, 0x0) REG INVARIANTS VIOLATION (false_reg1): range bounds violation u64=[0x7fffffff, 0x7ffffffd] s64=[0x7fffffff, 0x7ffffffd] u32=[0x7fffffff, 0x7ffffffd] s32=[0x7fffffff, 0x7ffffffd] var_off=(0x7fffffff, 0x0) REG INVARIANTS VIOLATION (false_reg2): const tnum out of sync with range bounds u64=[0x0, 0xffffffffffffffff] s64=[0x8000000000000000, 0x7fffffffffffffff] u32=[0x0, 0xffffffff] s32=[0x80000000, 0x7fffffff] var_off=(0x7fffffff, 0x0) 19: R6_w=0x7fffffff 20: (95) exit from 19 to 21: R0=0x7fffffff R6=scalar(smin=umin=smin32=umin32=2,smax=umax=smax32=umax32=0x7ffffffe,var_off=(0x2; 0x7ffffffd)) R7=map_ptr(ks=4,vs=8) R9=ctx() R10=fp0 fp-24=map_ptr(ks=4,vs=8) fp-40=mmmmmmmm 21: R0=0x7fffffff R6=scalar(smin=umin=smin32=umin32=2,smax=umax=smax32=umax32=0x7ffffffe,var_off=(0x2; 0x7ffffffd)) R7=map_ptr(ks=4,vs=8) R9=ctx() R10=fp0 fp-24=map_ptr(ks=4,vs=8) fp-40=mmmmmmmm 21: (14) w6 -= 2147483632 ; R6_w=scalar(smin=umin=umin32=2,smax=umax=0xffffffff,smin32=0x80000012,smax32=14,var_off=(0x2; 0xfffffffd)) 22: (76) if w6 s>= 0xe goto pc+1 ; R6_w=scalar(smin=umin=umin32=2,smax=umax=0xffffffff,smin32=0x80000012,smax32=13,var_off=(0x2; 0xfffffffd)) 23: (95) exit from 22 to 24: R0=0x7fffffff R6_w=14 R7=map_ptr(ks=4,vs=8) R9=ctx() R10=fp0 fp-24=map_ptr(ks=4,vs=8) fp-40=mmmmmmmm 24: R0=0x7fffffff R6_w=14 R7=map_ptr(ks=4,vs=8) R9=ctx() R10=fp0 fp-24=map_ptr(ks=4,vs=8) fp-40=mmmmmmmm 24: (14) w6 -= 14 ; R6_w=0 [...] What can be seen here is a register invariant violation on line 19. After the binary-or in line 18, the verifier knows that bit 2 is set but knows nothing about the rest of the content which was loaded from a map value, meaning, range is [2,0x7fffffff] with var_off=(0x2; 0x7ffffffd). When in line 19 the verifier analyzes the branch, it splits the register states in reg_set_min_max() into the registers of the true branch (true_reg1, true_reg2) and the registers of the false branch (false_reg1, false_reg2). Since the test is w6 != 0x7ffffffd, the src_reg is a known constant. Internally, the verifier creates a "fake" register initialized as scalar to the value of 0x7ffffffd, and then passes it onto reg_set_min_max(). Now, for line 19, it is mathematically impossible to take the false branch of this program, yet the verifier analyzes it. It is impossible because the second bit of r6 will be set due to the prior or operation and the constant in the condition has that bit unset (hex(fd) == binary(1111 1101). When the verifier first analyzes the false / fall-through branch, it will compute an intersection between the var_off of r6 and of the constant. This is because the verifier creates a "fake" register initialized to the value of the constant. The intersection result later refines both registers in regs_refine_cond_op(): [...] t = tnum_intersect(tnum_subreg(reg1->var_off), tnum_subreg(reg2->var_off)); reg1->var_o ---truncated---

AI Analysis

Technical Summary

CVE-2024-41003 is a vulnerability in the Linux kernel's eBPF (extended Berkeley Packet Filter) verifier component. The issue arises from a register invariant violation during the verification of eBPF programs, specifically in the reg_set_min_max function that manages register state ranges. The vulnerability was discovered through fuzzing techniques that revealed inconsistent range bounds and fake register states during branch condition analysis. The verifier incorrectly analyzes a branch that is mathematically impossible to take due to bitwise operations on register values, leading to corrupted internal state and potential misinterpretation of eBPF program logic. This flaw could allow crafted eBPF programs to bypass verifier checks, potentially enabling execution of malicious or unintended code within the kernel context. Since eBPF programs run with kernel privileges and are used for networking, tracing, and security monitoring, exploitation could lead to privilege escalation, kernel memory corruption, or denial of service. The vulnerability affects Linux kernel versions identified by the commit hashes provided, and has been publicly disclosed without a CVSS score or known exploits in the wild as of the publication date.

Potential Impact

For European organizations, this vulnerability poses a significant risk due to the widespread use of Linux in servers, cloud infrastructure, and embedded systems. Exploitation could allow attackers to execute arbitrary code at the kernel level, leading to full system compromise, data breaches, or disruption of critical services. Organizations relying on Linux-based network appliances, container hosts, or monitoring tools that utilize eBPF are particularly at risk. The ability to bypass the eBPF verifier undermines kernel security guarantees, potentially facilitating advanced persistent threats or ransomware attacks. Given the critical role of Linux in European telecommunications, finance, government, and industrial control systems, the impact could extend to national infrastructure and sensitive data environments. Although no active exploits are known, the complexity and privileged nature of the vulnerability warrant immediate attention to prevent future attacks.

Mitigation Recommendations

European organizations should promptly apply Linux kernel updates that include the patch for CVE-2024-41003 once available from their distribution vendors. Until patches are deployed, organizations can mitigate risk by restricting eBPF program loading to trusted users only, typically root or specific capabilities, and auditing eBPF usage on critical systems. Employing kernel lockdown features and mandatory access controls (e.g., SELinux, AppArmor) can limit the ability of unprivileged users to load or manipulate eBPF programs. Network segmentation and monitoring for unusual eBPF activity can help detect exploitation attempts. For environments using container orchestration, ensure that container runtimes do not grant unnecessary eBPF privileges. Additionally, organizations should maintain robust incident response plans to quickly address any suspicious kernel-level activity. Collaboration with Linux distribution maintainers and security communities is advised to stay informed about patch releases and exploit developments.