CVE-2026-77102: Commvault CommServe Buffer Overflow Flaw

CVE-2026-77102 Overview

CVE-2026-77102 is a heap-based buffer overflow [CWE-122] in Commvault CommServe that affects service availability. The vulnerability allows a remote, unauthenticated attacker to corrupt heap memory and disrupt the CommServe process. CommServe is the central management component of the Commvault data protection platform, so an outage propagates to backup and recovery operations across the environment. Commvault has published a security advisory and released a maintenance update that customers must apply to their CommServe installations.

Critical Impact
Remote unauthenticated attackers can trigger a heap-based buffer overflow in CommServe to cause a denial-of-service condition, halting backup, restore, and management operations.

Affected Products

Commvault CommServe (see vendor advisory CV_2026_08_4 for affected maintenance releases)
Commvault deployments running on Microsoft Windows
Commvault deployments running on Linux

Discovery Timeline

2026-09-08 - CVE-2026-77102 published to the National Vulnerability Database (NVD)
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-77102

Vulnerability Analysis

CVE-2026-77102 is classified as a heap-based buffer overflow [CWE-122] in the Commvault CommServe component. CommServe coordinates backup jobs, storage policies, and client communication across a Commvault cell, making it a high-value target. Successful exploitation corrupts adjacent heap metadata and structures, forcing the affected service into an unrecoverable state. The immediate consequence is loss of availability for the CommServe service and any workflow dependent on it, including scheduled backups and restore operations. The advisory scopes the impact to availability, with no reported effect on confidentiality or integrity of stored data.

Root Cause

The root cause is improper validation of the length of attacker-controlled input written into a heap-allocated buffer inside CommServe. When the input exceeds the buffer boundary, the write operation overruns the allocation and corrupts neighboring heap memory. Commvault has not published exploitation details beyond the advisory, and no public proof-of-concept is available.

Attack Vector

The vulnerability is reachable over the network with no authentication and no user interaction. An attacker with network access to the CommServe management interface can send a crafted request that triggers the overflow. Because CommServe often accepts connections from distributed MediaAgents and clients, network exposure is broad in typical deployments. Refer to the Commvault Security Advisory CV_2026_08_4 for vendor-published technical detail.

No verified exploit code is available. See the Commvault advisory for authoritative technical context.

Detection Methods for CVE-2026-77102

Indicators of Compromise

Unexpected termination or repeated restarts of the CommServe service on Windows or Linux hosts.
Crash dumps or Windows Application event log entries citing access violations in CommServe processes.
Failed or hung backup and restore jobs correlating with CommServe unavailability.
Inbound network traffic to CommServe management ports from untrusted or unmanaged sources.

Detection Strategies

Monitor CommServe process health and service state, and alert on abnormal termination or restart loops.
Inspect network traffic to CommServe endpoints for malformed or oversized protocol messages.
Correlate CommServe crash events with preceding network sessions to identify probable exploitation attempts.

Monitoring Recommendations

Forward CommServe application, system, and audit logs to a centralized SIEM for retention and correlation.
Enable process crash telemetry on the CommServe host and route it to your endpoint detection stack.
Track backup job success rates as a business-level signal for availability disruption caused by exploitation.

How to Mitigate CVE-2026-77102

Immediate Actions Required

Apply the CommServe maintenance release identified in Commvault Security Advisory CV_2026_08_4 as soon as change control permits.
Restrict network access to CommServe management interfaces to trusted MediaAgent, client, and administrative sources only.
Inventory all CommServe instances, including disaster recovery replicas, and verify patch status on each.

Patch Information

Commvault has released a resolved maintenance update for CommServe. Customers must upgrade CommServe to the fixed maintenance release documented in advisory CV_2026_08_4. Follow the vendor's standard CommServe upgrade procedure and validate service health after patching.

Workarounds

Place CommServe behind network segmentation or a firewall policy that allows only required source addresses to reach management ports.
Increase monitoring of CommServe availability and backup job outcomes until the patch is fully deployed.
Ensure offline or immutable backup copies exist so recovery is possible if CommServe availability is disrupted.

bash

# Example: restrict inbound access to CommServe management port on Linux (iptables)
iptables -A INPUT -p tcp --dport 8400 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8400 -j DROP