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In the Linux kernel, a NULL pointer dereference vulnerability was discovered in the traffic control subsystem’s IFE (Inter-Frame Encoding) action module (act_ife). The flaw resides in the `tcf_ife_encode()` function, which calls `ife_encode()` to prepare metadata for encoding into network packets. The code improperly assumed that `ife_encode()` would always return a valid pointer, failing to check for a possible NULL return value, which can occur due to memory allocation failures or specific error conditions. When `ife_encode()` returns NULL, the subsequent call to `ife_encode_meta_u32()` passes this NULL pointer to ife_tlv_meta_encode(). This results in a NULL pointer dereference when the function attempts to access memory at offset 0x0, as seen in the KASAN report. The issue was discovered by syzbot, a kernel fuzzing tool, which triggered a general protection fault. The crash trace shows the error propagating from `ife_tlv_meta_encode()` in `net/ife/ife.c` back through the IFE action and up the network stack’s queuing discipline (sch_multiq). An attacker with the ability to configure traffic control rules on a local system could potentially trigger this condition, causing a kernel panic and leading to a system crash (denial of service). The fix involves adding a simple NULL pointer check in `tcf_ife_encode()` to ensure the return value from `ife_encode()` is valid before it is used in any further operations .
Platform: Linux Kernel
Version: Multiple distributions
Vulnerability: NULL pointer dereference
Severity: 4.4 MEDIUM
date: 2026-02-04
Prediction: Patch already available
What Undercode Say:
This section provides analytics and technical commands related to CVE-2026-23064. The vulnerability highlights the critical importance of validating return values in kernel code, a common class of issues that can lead to system instability. The syzbot discovery underscores the value of automated fuzzing in identifying such edge cases. The impact is primarily on availability, making it a moderate-severity issue for systems that utilize the IFE action in their network traffic control configurations. The following commands and code snippets illustrate how to assess, protect, and understand the exploitability of this flaw.
Analytics:
Check if the act_ife module is currently loaded on your system lsmod | grep act_ife If the module is loaded, check its information (version, dependencies) modinfo act_ife Search kernel logs for the specific error signature mentioned in the CVE sudo dmesg | grep -E "tcf_ife_act|ife_tlv_meta_encode|general protection fault.act_ife" For Debian-based systems, check the status of the kernel package against the fixed version (e.g., for Debian 11, fixed in 5.10.249-1) apt-cache policy linux-image-$(uname -r) apt-cache policy linux-image-amd64 For Red Hat-based systems, check if the current kernel is vulnerable uname -r Then cross-reference with security advisories from your distribution
Exploit:
// The vulnerability is triggered in the kernel code path shown below. // No public user-space exploit is detailed, but the crash trace reveals the exact call chain. // The following is the vulnerable call stack from the original report: ife_tlv_meta_encode+0x41/0xa0 net/ife/ife.c:166 ife_encode_meta_u32+0x153/0x180 net/sched/act_ife.c:101 tcf_ife_encode net/sched/act_ife.c:841 [bash] tcf_ife_act+0x1022/0x1de0 net/sched/act_ife.c:877 // An attacker would need to create a traffic control (tc) configuration // using the IFE action that forces ife_encode() to return NULL. // This could potentially be achieved by causing resource exhaustion or // providing specific invalid metadata parameters during packet encoding.
Protection from this CVE:
The primary protection is to apply the kernel patch. Update your system. For Debian/Ubuntu: sudo apt update && sudo apt upgrade linux-image-$(uname -r) For RHEL/CentOS/Fedora: sudo yum update kernel or sudo dnf update kernel As a temporary workaround, if IFE action is not required: Unload the vulnerable module sudo modprobe -r act_ife Permanently blacklist the module to prevent it from loading on boot echo "blacklist act_ife" | sudo tee /etc/modprobe.d/blacklist-ife.conf Remove any existing IFE actions from traffic control configurations sudo tc actions flush action ife If the module is required, consider restricting local access to configure traffic control to trusted users only, as the vulnerability requires local ability to set up tc rules .
Impact:
Successful exploitation of this vulnerability leads to a kernel NULL pointer dereference. This causes a general protection fault and results in a kernel panic, effectively crashing the system. The primary impact is on system availability, creating a denial-of-service (DOS) condition. According to the CVSS vector from SUSE (CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H), the attack vector is local, requires high privileges, but has no impact on confidentiality or integrity. Systems that do not use the IFE action in their network traffic control (tc) configurations are not exposed to this flaw. The vulnerability does not allow for privilege escalation or arbitrary code execution, but its exploitation can render the machine unusable until rebooted .
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Reported By: nvd.nist.gov
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