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CVE-2026-16873 is a local privilege escalation vulnerability affecting IBM AIX versions 7.2 and 7.3, as well as IBM PowerVM VIOS version 4.1. The flaw stems from an out-of-bounds write (CWE-787) in the kernel, which allows a local attacker to overwrite critical control data in memory.
The vulnerability arises when a malicious local user triggers an overflow that writes data past the end—or before the beginning—of an intended buffer. This out-of-bounds write corrupts kernel memory structures, enabling the attacker to bypass operating system safeguards and execute arbitrary code with elevated privileges. Because the flaw resides in the kernel, a successful exploit grants full control over the confidentiality, integrity, and availability of the affected system.
Attackers must have local access to the target system, meaning the vulnerability cannot be exploited remotely. However, once local access is obtained, the exploitation is considered easy. The CVSS base score assigned by IBM is 7.8 (HIGH), with the vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Third-party assessments rate the severity as “very critical” with a meta score of 8.3.
Affected systems include IBM AIX 7.2 and 7.3 across all tenant levels up to TL04, as well as PowerVM VIOS 4.1.0, 4.1.1, and 4.1.2. IBM has released cumulative fixes through Service Packs and Fix Packs: AIX 7.3 TL04 SP2, TL03 SP3, TL02 SP5; AIX 7.2 TL05 SP13; VIOS 4.1.2.20, 4.1.1.30, and 4.1.0.50. These patches are available via IBM Fix Central and require a system reboot unless Live Update is used on AIX.
As of the publication date, no public exploit is available, and the vulnerability is not listed in the CISA KEV catalog. However, the estimated exploit price on underground markets ranges from $5,000 to $25,000, indicating active interest from attackers. Immediate patching is strongly recommended to reduce the attack surface.
DailyCVE Form:
Platform: IBM AIX/PowerVM VIOS
Version: 7.2,7.3,4.1
Vulnerability: Out-of-bounds write
Severity: HIGH (7.8)
Date: 08/19/2026
Prediction: 08/21/2026
What Undercode Say:
The following analytics provide insight into the vulnerability’s impact and remediation status.
Check AIX version and TL level oslevel -s Check installed VIOS fix pack level ioslevel Verify if system is vulnerable (AIX 7.2, 7.3 up to TL04) instfix -ik | grep -E "IJ59566|IJ59565|IJ59564|IJ59563" Check for available APARs lslpp -L | grep -E "IJ59566|IJ59565|IJ59564|IJ59563" Download fixes from IBM Fix Central (example) https://www.ibm.com/support/fixcentral Apply AIX Service Pack (example for 7.3 TL04 SP2) inutoc /path/to/SP smitty update_all Apply VIOS Fix Pack (example for 4.1.2.20) updateios -install /path/to/fixpack -accept -reboot
Exploit: (Educational Purposes!)
A local attacker can exploit this vulnerability by crafting a malicious program that triggers an out-of-bounds write in the kernel. The exploit typically involves:
1. Identifying a kernel function or syscall that handles user-supplied input without proper bounds checking.
2. Supplying oversized or malformed input to cause the kernel to write beyond the allocated buffer.
3. Overwriting adjacent kernel memory, such as function pointers, process credentials, or security tokens.
4. Escalating privileges by modifying the attacker’s process credentials to root (UID 0).
While no public exploit exists, proof-of-concept code would likely leverage standard local privilege escalation techniques, including memory spraying and return-oriented programming (ROP) to gain full system control.
Protection:
- Apply the recommended IBM Service Packs and Fix Packs immediately.
- For AIX 7.3: install TL04 SP2, TL03 SP3, or TL02 SP5.
- For AIX 7.2: install TL05 SP13.
- For VIOS 4.1: install 4.1.2.20, 4.1.1.30, or 4.1.0.50.
- Use IBM Fix Central to download patches: https://www.ibm.com/support/fixcentral.
- Reboot the LPAR after applying updates, or use Live Update on AIX to avoid downtime.
- Restrict local access to trusted users only.
- Monitor system logs for unusual activity or unauthorized privilege escalation attempts.
Impact:
A successful exploit grants the attacker full root-level control over the affected system. This compromises the confidentiality, integrity, and availability of the system, allowing the attacker to read sensitive data, modify system files, install backdoors, or disrupt operations. Given the local access requirement, the impact is limited to environments where untrusted users have shell access, but in shared or multi-tenant systems, the risk is significantly elevated.
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Sources:
Reported By: nvd.nist.gov
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