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CVE-2026-15961 is a medium-severity vulnerability identified in the IBM PowerVM Hypervisor firmware. The flaw resides in the improper control of externally-supplied format strings, a weakness classified under CWE-134. This issue affects specific firmware versions: FW1120.00, FW1110.00 through FW1110.30, and FW1060.00 through FW1060.80.
Format string vulnerabilities arise when user-controlled input is used directly as the format string argument in functions like `printf()` or syslog(). In the context of the PowerVM Hypervisor, a local attacker with high privileges could craft malicious input that is passed unsafely to such a function. Because the hypervisor handles critical system operations, this flaw can be exploited to read from or write to arbitrary memory locations.
By leveraging this vulnerability, an attacker could achieve two primary outcomes. First, they could obtain sensitive information from kernel memory, potentially including cryptographic keys, passwords, or memory addresses that could be used to bypass other security mechanisms. Second, they could cause a denial of service (DoS) by corrupting memory or triggering a system crash. The exploitation requires local access and high privileges, but the impact on system availability is rated as high.
The vulnerability has been assigned a CVSS 3.1 base score of 5.2 (Medium) by IBM, with a vector of AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H. NIST has also provided a separate CVSS calculation with a score of 6.0 (Medium), reflecting a slightly lower attack complexity (AC:L) and higher confidentiality impact (C:H). As of the publication date, no official patch has been released by IBM.
DailyCVE Form:
Platform: IBM PowerVM
Version: FW1120.00, FW1110.00-FW1110.30, FW1060.00-FW1060.80
Vulnerability: Format String (CWE-134)
Severity: Medium (CVSS 5.2)
date: August 19, 2026
Prediction: September 2026
What Undercode Say:
The following commands can be used to check the firmware version on an IBM Power System to determine if it is affected by CVE-2026-15961.
Check the current system firmware level
lssyscfg -r sys -F "fw_level"
Alternative method to view firmware version
lsfirmware -v
Check for specific vulnerable versions
lssyscfg -r sys -F "fw_level" | grep -E "FW1120.00|FW1110.[0-9]{2}|FW1060.[0-9]{2}"
Exploit: (Educational Purposes!)
A local attacker with high privileges could attempt to trigger the format string vulnerability by passing maliciously crafted input to a hypervisor function that unsafely handles format strings. The following conceptual snippet demonstrates how unsanitized user input can lead to memory read or write primitives:
// Vulnerable code pattern (conceptual)
void hypervisor_log(char user_input) {
char buffer[bash];
sprintf(buffer, user_input); // Unsafe: user_input used as format string
// Attacker can use %x, %n, %s to read/write memory
}
// Example exploitation to read stack memory
// Input: "%x %x %x %x" would leak stack values
Protection:
Until an official fix is released by IBM, the primary mitigation is to restrict local access to only trusted users with high privileges. Administrators should monitor IBM’s security advisory page (`https://www.ibm.com/support/pages/node/7283228`) for patch availability. Additionally, enabling system auditing and intrusion detection can help identify anomalous local activity that may indicate exploitation attempts.
Impact:
Successful exploitation of this vulnerability could allow a local attacker to read sensitive information from hypervisor memory, potentially compromising the confidentiality of the entire virtualized environment. Furthermore, the attacker could cause a denial of service, rendering the hypervisor and all hosted logical partitions (LPARs) unavailable. The CVSS score indicates high availability impact, meaning system crashes or prolonged downtime are likely outcomes of a successful attack.
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Sources:
Reported By: nvd.nist.gov
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