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CVE-2026-16891 is an out-of-bounds read vulnerability affecting IBM AIX versions 7.2 and 7.3, as well as IBM PowerVM VIOS version 4.1. The vulnerability resides in the way these operating systems handle certain memory operations, allowing a local attacker to read memory locations beyond the intended boundaries of a buffer.
At the core of this issue is a failure in input validation or bounds checking within a system component or service. When a local user executes a specific sequence of operations or provides specially crafted input, the affected code attempts to access memory that has not been allocated for the current process or that lies outside the valid range of the buffer in question. This is classified under CWE-125 (Out-of-bounds Read).
The vulnerability requires local access to the target system, meaning the attacker must already have an authenticated session or the ability to execute commands on the affected AIX or VIOS environment. The attack vector is local (AV:L), the attack complexity is low (AC:L), and the privileges required are low (PR:L). No user interaction is needed (UI:N).
Once exploited, the out-of-bounds read allows the attacker to read sensitive information from adjacent memory regions. This could include cryptographic keys, session tokens, authentication credentials, configuration data, or other confidential information belonging to other processes or the kernel itself. The impact is limited to confidentiality (C:L) with no impact on integrity (I:N) or availability (A:N).
The vulnerability is not remotely exploitable, and there is no known privilege escalation or code execution component associated with this flaw. The CVSS base score assigned by IBM is 3.3, which is rated as LOW severity. The vulnerability was published on August 19, 2026, and last modified on August 20, 2026.
IBM has acknowledged the issue and assigned APARs (Authorized Program Analysis Reports) to track the fixes. The fixes are cumulative and included in specific Service Packs for AIX and Fix Packs for VIOS. An LPAR reboot is required to complete the update, though AIX Live Update can be used to avoid a reboot.
DailyCVE Form:
Platform: IBM AIX, PowerVM VIOS
Version: 7.2, 7.3, 4.1
Vulnerability: Out-of-bounds Read
Severity: LOW (CVSS 3.3)
date: August 19, 2026
Prediction: August 14, 2026 (Fix Available)
What Undercode Say:
Check current AIX version oslevel -s Check current VIOS version ioslevel Verify if system is affected (AIX 7.2, 7.3 or VIOS 4.1) uname -a Download fixes from IBM Fix Central https://www.ibm.com/support/fixcentral For AIX 7.3 TL04 SP2 (contains fix) For AIX 7.3 TL03 SP3 (contains fix) For AIX 7.3 TL02 SP5 (contains fix) For AIX 7.2 TL05 SP13 (contains fix) For VIOS 4.1.2.20 (contains fix) For VIOS 4.1.1.30 (contains fix) For VIOS 4.1.0.50 (contains fix) Preview fix installation installp -a -d fix_name -p all Install fix installp -a -d fix_name -x all Verify fix installation lslpp -L | grep -i fix_name Reboot required after installation shutdown -Fr
Exploit: (Educational Purposes!)
No public proof-of-concept exploit code is currently available for CVE-2026-16891. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog, suggesting no weaponized exploit is known to exist. Exploitation would require:
1. Local authenticated access to an affected AIX 7.2/7.3 or VIOS 4.1 system
2. Crafting specific input or invoking a vulnerable system function
3. Triggering an out-of-bounds read to leak adjacent memory contents
The attack complexity is low, and the privileges required are low, making the barrier to exploitation minimal for local attackers. However, the impact is limited to confidentiality disclosure without privilege escalation or remote code execution capabilities.
Protection:
- Apply the official IBM fixes immediately. The following cumulative Service Packs and Fix Packs contain the remediation:
– AIX 7.3 TL04 SP2
– AIX 7.3 TL03 SP3
– AIX 7.3 TL02 SP5
– AIX 7.2 TL05 SP13
– VIOS 4.1.2.20
– VIOS 4.1.1.30
– VIOS 4.1.0.50
2. Download fixes from IBM Fix Central: https://www.ibm.com/support/fixcentral
3. Verify fix integrity using OpenSSL signatures before installation:
openssl dgst -sha256 [bash]
4. Create a mksysb backup before applying fixes:
mksysb -i /dev/rmt0
5. Restrict local access to AIX and VIOS systems to minimize exposure
6. Monitor system logs for unusual memory access patterns or unauthorized local activity
Impact:
- Confidentiality: Local attackers can read sensitive information from memory, potentially exposing cryptographic keys, session tokens, authentication credentials, and configuration data
- Integrity: No direct integrity impact; the vulnerability only allows reading, not modification, of data
- Availability: No availability impact; the vulnerability does not cause system crashes or denial of service
- Scope: Limited to local authenticated users; no remote exploitation pathway
- Severity: LOW (CVSS 3.3) due to limited impact and local access requirement
- Affected Systems: IBM AIX 7.2, IBM AIX 7.3, and IBM PowerVM VIOS 4.1
- Remediation: Cumulative fixes available as of August 14, 2026; LPAR reboot required
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Sources:
Reported By: nvd.nist.gov
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