# Titles:** Linux Kernel Local Privilege Escalation (CVE-2026-43284 / CVE-2026-43500 / CVE-2026-46300) # Author:** nu11secur1ty # Date:** 2026-05-11 # Vendor:** Linux Kernel # Software:** Linux Kernel (All major distributions) # Vulnerability Type:** Page-Cache Write / Memory Corruption # Status:** HIGH / CRITICAL --- ## Description The **"Kukurigu"** exploit represents a sophisticated local privilege escalation (LPE) vector targeting the Linux kernel's page-cache management. The vulnerability is not a single bug, but a strategic chain of two distinct flaws that allow an unprivileged attacker to bypass standard filesystem write protections. ### Vulnerability Chain: 1. **CVE-2026-43284 (xfrm-ESP):** A logic error in the ESP protocol implementation when Extended Sequence Numbers (ESN) are active. This flaw allows a local user to perform arbitrary 4-byte writes directly into the page-cache. 2. **CVE-2026-43500 (RxRPC):** A flaw in the RxRPC protocol that facilitates in-place decryption of data within page-cache pages. 3. **CVE-2026-46300 (Fragnesia - ESP-in-TCP):** A bug in `skb_try_coalesce()` allowing page-cache write via fragmented ESP packets. ### Impact Analysis: By chaining these vulnerabilities, an attacker can modify the memory-resident pages of setuid binaries (e.g., `/usr/bin/su` or `/usr/bin/sudo`) or sensitive system files (e.g., `/etc/passwd`). Because the modification occurs in the page-cache, the attacker effectively "poison" the execution environment. **Key Advantages for Attacker:** * **Stability:** No race conditions involved. * **Reliability:** Near 100% success rate on tested environments. * **Stealth:** Does not trigger kernel panics or system instability upon failure. * **Persistence:** Affects kernels spanning nearly 9 years (2017-01-17 to 2026-05-10). --- ## Affected Systems (Verified) The following distributions have been tested and confirmed vulnerable: * **Ubuntu:** 24.04.4 / 25.10 / 26.04 * **RHEL:** 10.1 * **openSUSE:** Tumbleweed * **CentOS Stream:** 10 * **AlmaLinux:** 10 * **Fedora:** 44 --- ## Proof of Concept (PoC) ### Execution Flow: ```bash # Compiling the exploit tool $ gcc -O2 kukurigu.c -o kukurigu_exploit # Running the exploit against a target binary $ ./kukurigu_exploit --target /usr/bin/su --method esp [+] Initializing Kukurigu LPE engine... [+] Exploiting CVE-2026-43284 (xfrm-ESP write)... [+] Exploiting CVE-2026-43500 (RxRPC decryption)... [+] Exploiting CVE-2026-46300 (Fragnesia)... [+] Page-cache poisoned successfully for /usr/bin/su. [+] Dropping into root shell... # id uid=0(root) gid=0(root) groups=0(root) [+]Exploit: [href](https://github.com/nu11secur1ty/CVE-mitre/tree/main/2026/CVE-2026-43284-CVE-2026-43500) # Demo: [href](https://www.patreon.com/posts/cve-2026-43284-157962202) [href](https://www.patreon.com/posts/cve-2026-46300-k-158433402) # Patch if you want: [href](https://www.patreon.com/posts/cve-2026-43284-157966167) # Time spent: 01:30:00 -- System Administrator - Infrastructure Engineer Penetration Testing Engineer Exploit developer at https://packetstormsecurity.com/ https://cve.mitre.org/index.html https://cxsecurity.com/ and https://www.exploit-db.com/ home page: https://www.asc3t1c-nu11secur1ty.com/ hiPEnIMR0v7QCo/+SEH9gBclAAYWGnPoBIQ75sCj60E= nu11secur1ty <https://www.asc3t1c-nu11secur1ty.com/>