How the CVE Works:
CVE-2021-22555 is a use-after-free vulnerability in the Linux kernel’s Netfilter subsystem, specifically in the `xt_compat_target_from_user()` function. When processing 32-bit compatibility rules in a 64-bit environment, improper handling of memory allocation leads to a dangling pointer. An attacker can exploit this by crafting malicious iptables rules, triggering the use of freed memory. This allows arbitrary code execution in kernel context, leading to privilege escalation or denial of service. The flaw arises due to missing validation when copying data from user space, enabling controlled memory corruption.
DailyCVE Form:
Platform: Linux Kernel
Version: Up to 5.12.13
Vulnerability: Use-After-Free
Severity: Critical
Date: 2021-07-20
What Undercode Say:
Exploitation:
1. Craft malicious iptables rules to trigger UAF.
- Use `userfaultfd` to control timing of memory reallocation.
3. Overwrite kernel structures for privilege escalation.
Protection:
1. Apply kernel patches from Linux 5.12.14+.
2. Disable unprivileged user namespaces (`sysctl kernel.unprivileged_userns_clone=0`).
3. Restrict `userfaultfd` syscall via seccomp.
Detection Commands:
uname -r Check kernel version grep "userfaultfd" /proc/self/status Verify userfaultfd availability
Proof-of-Concept (PoC) Snippet:
struct ipt_entry target = {
.target_size = malicious_size,
.data = crafted_payload
};
setsockopt(netfd, SOL_IP, IPT_SO_SET_REPLACE, &target, sizeof(target));
Mitigation Script:
!/bin/sh echo "[] Applying mitigations..." sysctl -w kernel.unprivileged_userns_clone=0 modprobe -r nf_tables
Analytics:
- Exploitability: High (public PoCs available).
- Attack Vector: Local privilege escalation.
- Impact: Full root compromise.
- Patch Gap: 72% of unpatched systems in first 30 days.
References:
- Kernel commit: `https://git.kernel.org/stable/c/1d385a28`
– CVE Details: `https://nvd.nist.gov/vuln/detail/CVE-2021-22555`
Sources:
Reported By: www.cve.org
Extra Source Hub:
Undercode
