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The vulnerability resides in the PowerVM hypervisor call interface, a critical component that handles privileged instructions from logical partitions (LPARs). The affected firmware versions include FW1120.00, FW1110.00 through FW1110.30, FW1060.00 through FW1060.80, and FW950.00 through FW950.H2. An attacker with root-level access to a guest partition can craft a specific hypervisor call that exploits an improper array index validation (CWE-129). The hypervisor uses array-based tables to manage virtual processor states and scheduling data, and the call interface fails to sanitize an index parameter supplied by the caller. When a malicious index is provided, the hypervisor dereferences memory outside the intended array bounds. This out-of-bounds access does not allow attacker-controlled data writes but causes the virtual processor to enter an inconsistent state. The inconsistent state triggers a permanent hang of the targeted virtual processor, making it completely unresponsive to any further scheduling or interrupt requests. Normal recovery requires a full platform re-IPL (Initial Program Load), which involves rebooting the entire physical system, leading to significant downtime for all hosted partitions. In a minority of cases, the out-of-bounds read may inadvertently copy a small amount of hypervisor or partition memory into unexpected locations, but the attacker has no control over the target offset or the copied data. The attack vector is local (AV:L) as it requires authenticated root access within a guest, reducing the privilege requirement to High or Low depending on the configuration vector (PR:H or PR:L). The scope is changed (S:C) because the vulnerability impacts the hypervisor, which is a separate security boundary from the guest. Integrity impact is low (I:L) due to the uncontrolled data injection, while availability impact is high (A:H) because of the permanent processor hang. The official CVSS v3.1 base score is 7.1, categorized as High severity. IBM has acknowledged the flaw and provided firmware updates, but administrators must proactively apply them. Exploitation does not require user interaction (UI:N) and can be triggered repeatedly to degrade the entire managed system. The vulnerability was discovered internally by IBM’s security team and disclosed through their standard advisory process. Given the requirement for guest root privileges, the real-world exposure is somewhat mitigated in environments with strict partition administration controls. However, cloud or multi-tenant PowerVM deployments face elevated risk if tenants can gain root inside their LPARs. The primary security impact is denial of service, which can be weaponized to disrupt critical production workloads. The affected hardware families include Power System S, L, and E series spanning multiple generations. IBM has released fixed firmware revisions that correct the array index validation logic, ensuring the hypervisor rejects malformed call parameters.
DailyCVE Form:
Platform: IBM PowerVM Hypervisor
Version: FW1120.00, FW1110.00-30, FW1060.00-80, FW950.00-H2
Vulnerability: Improper Array Index Validation (CWE-129)
Severity: 7.1 High (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:H)
date: 2023-08-03
Prediction: Patch released in FW1110.31, FW1060.81, FW950.H3, and FW1120.01 (August 2023)
What Undercode Say:
Check current PowerVM firmware version
lsfirmware -a | grep "Version"
Alternative method via HMC
lshmc -V | grep "Firmware"
Validate against vulnerable ranges
FW=$(lsfirmware -a | grep "Version" | awk '{print $NF}')
if [[ $FW =~ ^FW1120.00$ || ($FW =~ ^FW1110. && $(echo $FW | cut -d. -f2) -le 30) || ($FW =~ ^FW1060. && $(echo $FW | cut -d. -f2) -le 80) || ($FW =~ ^FW950. && [[ $FW < "FW950.H3" ]]) ]]; then echo "Vulnerable to CVE-2023-31056"; else echo "Not vulnerable"; fi
Monitor for suspicious hypervisor calls in system logs
errpt -a | grep -i "hypervisor" | tail -20
Check for processor offline events that may indicate exploitation
lsdev -C | grep -E "proc|vcpu" | grep "Defined"
Exploit: (Educational Purposes!)
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</dt> <dt>// Conceptual demonstration of the hypercall with a malformed array index</dt> <dt>include <sys/ioctl.h></dt> <dt>include <linux/ppc64-papr.h> // PowerVM hypercall definitions</dt> <dt>define H_CALL 0x3A // Example hypercall number (actual number varies)</dt> <dt>define MALICIOUS_INDEX 0xFFFFFFFF // Out-of-bounds index</dt> <dt>long hypercall_handler(unsigned long call_id, unsigned long arg1, unsigned long arg2) {</dt> <dt>// In a real exploit, the attacker (root in guest) uses the "hcall" instruction</dt> <dt>// to invoke the hypervisor with a crafted index parameter.</dt> <dt>// The hypervisor does not validate this index before accessing an array:</dt> <dt>// struct vcpu_sched table = get_sched_table();</dt> <dt>// table[bash] = ...; // Causes processor hang</dt> <dt>}</dt> <dt>int main() {</dt> <dt><strong>asm</strong> volatile (</dt> <dt>"li %%r3, %0\n" // Hypercall ID</dt> <dt>"li %%r4, %1\n" // Argument: malicious index</dt> <dt>"sc 1\n" // System call to trap into hypervisor</dt> <dd>: "i"(H_CALL), "r"(MALICIOUS_INDEX) : "r3","r4" ); return 0; }
Protection:
Immediately upgrade firmware to FW1110.31, FW1060.81, FW950.H3, or FW1120.01 and above. Limit root access inside guest partitions by enforcing strict privilege separation and using role-based access control. Implement system monitoring to detect unexpected partition panics or virtual processor hang events, and review IBM security bulletin IBMSEC-2023-XXXX for additional hardening guidelines. Consider using HMC’s “virtual processor state” checks to proactively identify unresponsive VCPUs and isolate potentially compromised guests.
Impact:
Successful exploitation results in a permanent hang of the affected virtual processor, forcing a full platform re-IPL that disrupts all running partitions and causes extended downtime (Availability: High). In rare cases, an uncontrolled out‑of‑bounds read may inject a small, non‑arbitrary data blob into hypervisor or partition memory, but the attacker cannot direct the write target, limiting Integrity impact to Low. No confidentiality loss occurs (Confidentiality: None). The vulnerability can be leveraged repeatedly by a malicious guest administrator to degrade the entire physical host, making it a potent denial‑of‑service weapon in shared environments.
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Sources:
Reported By: nvd.nist.gov
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