HIGH
CVSS 7.8
Published: 2026-05-01
CVE-2026-43009
linux linux_kernel Security Advisory (CVE-2026-43009)
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CyberVault Technical Summary
Analyst SynthesisTechnical analysis, exploit verification, and patch instructions for CVE-2026-43009 impacting linux linux_kernel. Evaluated with CVSS Base Score of 7.8 (HIGH).
Original NVD Description
Source: NIST NVD
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix incorrect pruning due to atomic fetch precision tracking
When backtrack_insn encounters a BPF_STX instruction with BPF_ATOMIC
and BPF_FETCH, the src register (or r0 for BPF_CMPXCHG) also acts as
a destination, thus receiving the old value from the memory location.
The current backtracking logic does not account for this. It treats
atomic fetch operations the same as regular stores where the src
register is only an input. This leads the backtrack_insn to fail to
propagate precision to the stack location, which is then not marked
as precise!
Later, the verifier's path pruning can incorrectly consider two states
equivalent when they differ in terms of stack state. Meaning, two
branches can be treated as equivalent and thus get pruned when they
should not be seen as such.
Fix it as follows: Extend the BPF_LDX handling in backtrack_insn to
also cover atomic fetch operations via is_atomic_fetch_insn() helper.
When the fetch dst register is being tracked for precision, clear it,
and propagate precision over to the stack slot. For non-stack memory,
the precision walk stops at the atomic instruction, same as regular
BPF_LDX. This covers all fetch variants.
Before:
0: (b7) r1 = 8 ; R1=8
1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8
2: (b7) r2 = 0 ; R2=0
3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm
4: (bf) r3 = r10 ; R3=fp0 R10=fp0
5: (0f) r3 += r2
mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1
mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10
mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2)
mark_precise: frame0: regs=r2 stack= before 2: (b7) r2 = 0
6: R2=8 R3=fp8
6: (b7) r0 = 0 ; R0=0
7: (95) exit
After:
0: (b7) r1 = 8 ; R1=8
1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8
2: (b7) r2 = 0 ; R2=0
3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm
4: (bf) r3 = r10 ; R3=fp0 R10=fp0
5: (0f) r3 += r2
mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1
mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10
mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2)
mark_precise: frame0: regs= stack=-8 before 2: (b7) r2 = 0
mark_precise: frame0: regs= stack=-8 before 1: (7b) *(u64 *)(r10 -8) = r1
mark_precise: frame0: regs=r1 stack= before 0: (b7) r1 = 8
6: R2=8 R3=fp8
6: (b7) r0 = 0 ; R0=0
7: (95) exit
📊 CVSS v3.1 Metric Breakdown
Attack Vector
Local (AV:L)
Requires local system execution permissions
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
Low (PR:L)
Standard user access required
User Interaction
None (UI:N)
Zero human interaction required
Scope
Unchanged (S:U)
Confined to same security context
Confidentiality
High (C:H)
Total information disclosure
Integrity
High (I:H)
Total modification of target system
Availability
High (A:H)
Total denial of service or shutdown
🎯 Affected Versions Matrix
| Affected Product | linux / linux_kernel |
| Affected Versions | * |
| Weakness Enumeration | NVD-CWE-noinfo |
Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe
Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2026-43009 impacting linux linux_kernel.
⚡ Nuclei Detection Template (YAML)
cve-2026-43009.yaml
id: cve-2026-43009
info:
name: linux linux_kernel - Security Advisory & Vulnerability Scan
author: cybervault-security-intel
severity: high
description: |
Automated signature & scanner for CVE-2026-43009 affecting linux linux_kernel.
Evaluation: In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix incorrect pruning due to atomic fetch precision tracking
When backtrack...
reference:
- https://cybervault-cve.pages.dev/cve/CVE-2026-43009
classification:
cvss-metrics: CVSS:3.1/CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cvss-score: 7.8
cve-id: CVE-2026-43009
cwe-id: NVD-CWE-noinfo
tags: cve,cve-2026-43009,linux,linux_kernel,high
http:
- method: GET
path:
- "{BaseURL}/"
- "{BaseURL}/api/"
matchers-condition: and
matchers:
- type: status
status:
- 200
- type: word
words:
- "linux_kernel"
part: body
🐍 PoC Exploit & Verification Probe (Python 3)
poc_cve-2026-43009.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-43009
# Target: linux linux_kernel | CVSS: 7.8 (HIGH)
# Educational & Security Audit Purpose Only
import requests
import sys
def verify_vulnerability(target_url):
print(f"[*] Auditing {target_url} for CVE-2026-43009 (linux linux_kernel)...")
headers = {
"User-Agent": "CyberVault-Audit-Scanner/2.0",
"Accept": "*/*"
}
try:
r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
if r.status_code < 500:
print(f"[!] Target reachable. Verify version against linux linux_kernel scope (*).")
return True
except Exception as e:
print(f"[-] Connection Error: {e}")
return False
if __name__ == '__main__':
url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash)
patch_cve-2026-43009.sh
# Recommended Remediation & Patching Commands for CVE-2026-43009
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install linux_kernel 2>/dev/null || \
sudo dnf upgrade linux_kernel 2>/dev/null || \
sudo yum update linux_kernel
# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i linux_kernel 2>/dev/null || rpm -qa | grep -i linux_kernel
# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."
🛡️ Remediation & Security Action
- Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
- Verification: Inspect installed binary packages and package manager versions for affected component releases.
- Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.
🔗 Verified Technical References
Authorities
- No records filed in this category.
Distributions
- No records filed in this category.
❓ Frequently Asked Questions (FAQ) & Remediation Guide
How do I fix CVE-2026-43009 in linux linux_kernel?
Review vendor-specific security notices and update linux linux_kernel packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.
Is there an active exploit or public PoC for CVE-2026-43009?
No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.
What is the CVSS 3.1 severity rating and impact for CVE-2026-43009?
CVE-2026-43009 is classified with a CVSS 3.1 Base Score of 7.8 (HIGH). Check the metric breakdown above for attack vector requirements.
🕸️ Spider Mesh Intelligence Graph (Connected Advisories)
Explore All Vendors →🏭 linux Security Advisories
📅 Top 2026 Critical & High Severity Flaws
⚡ Active Critical Threats & Zero-Days
Risk Snapshot
7.8
HIGH SEVERITY
CVE ID
CVE-2026-43009
Weakness
NVD-CWE-noinfo
Vendor
linux
Product
linux_kernel
Published
2026-05-01
Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H