{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-45933",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2026-45933"
  ],
  "published": "2026-05-27T12:19:29Z",
  "summary": "bpf: Preserve id of register in sync_linked_regs()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Preserve id of register in sync_linked_regs()\n\nsync_linked_regs() copies the id of known_reg to reg when propagating\nbounds of known_reg to reg using the off of known_reg, but when\nknown_reg was linked to reg like:\n\nknown_reg = reg         ; both known_reg and reg get same id\nknown_reg += 4          ; known_reg gets off = 4, and its id gets BPF_ADD_CONST\n\nnow when a call to sync_linked_regs() happens, let's say with the following:\n\nif known_reg >= 10 goto pc+2\n\nknown_reg's new bounds are propagated to reg but now reg gets\nBPF_ADD_CONST from the copy.\n\nThis means if another link to reg is created like:\n\nanother_reg = reg       ; another_reg should get the id of reg but\n                          assign_scalar_id_before_mov() sees\n                          BPF_ADD_CONST on reg and assigns a new id to it.\n\nAs reg has a new id now, known_reg's link to reg is broken. If we find\nnew bounds for known_reg, they will not be propagated to reg.\n\nThis can be seen in the selftest added in the next commit:\n\n0: (85) call bpf_get_prandom_u32#7    ; R0=scalar()\n1: (57) r0 &= 255                     ; R0=scalar(smin=smin32=0,smax=umax=smax32=umax32=255,var_off=(0x0; 0xff))\n2: (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))\n3: (07) r1 += 4                       ; R1=scalar(id=1+4,smin=umin=smin32=umin32=4,smax=umax=smax32=umax32=259,var_off=(0x0; 0x1ff))\n4: (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))\n5: (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)\n6: (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))\n7: (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))\n8: (37) r0 /= 0\ndiv by zero\n\nWhen 4 is verified, r1's bounds are propagated to r0 but r0 also gets\nBPF_ADD_CONST (bug).\nWhen 5 is verified, r0 gets a new id (2) and its link with r1 is broken.\n\nAfter 6 we know r1 has bounds [14, 259] and therefore r0 should have\nbounds [10, 255], therefore the branch at 7 is always taken. But because\nr0's id was changed to 2, r1's new bounds are not propagated to r0.\nThe verifier still thinks r0 has bounds [6, 255] before 7 and execution\ncan reach div by zero.\n\nFix this by preserving id in sync_linked_regs() like off and subreg_def.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-45933"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/58059335e46537de682db84984f7716c813208c4"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/92a8cb1806adefb263cf096eab6705705cf7eee1"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/65d114b5270b62aefb820ecd6c3b7caeea8f895d"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/af9e89d8dd39530c8bd14c33ddf6b502df1071b6"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T13:16:28Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The bug is in the BPF verifier, reached only by loading a crafted BPF program via the bpf() syscall from a local process; remote data never reaches this code.\nAC:L - The attacker writes the exact BPF instruction sequence that deterministically triggers the broken link in sync_linked_regs(); no race or uncontrolled condition is involved.\nPR:L - The verifier runs for all program loads, and socket-filter/cgroup-skb programs are loadable without CAP_BPF when unprivileged_bpf_disabled=0 (a supported default), so any unprivileged local user can reach it.\nUI:N - The attacker loads and runs their own program; no victim action is required.\nS:U - Impact is confined to the kernel's own security authority \u2014 standard local privilege escalation, no crossing into a separate VM/IOMMU boundary.\nC:H - The verifier can be made to believe a register holds a wrong value, allowing a verified-as-safe out-of-bounds read primitive over kernel memory, yielding arbitrary kernel memory disclosure.\nI:H - The same false-bounds primitive enables an out-of-bounds write the verifier \"proved\" safe, giving an arbitrary kernel write usable for privilege escalation and code-flow hijacking.\nA:H - The resulting out-of-bounds accesses on attacker-controlled values readily corrupt kernel memory and panic/crash the system."
    }
  }
}