CVE-2026-77101: Commvault CommServe Buffer Overflow Vulnerability

CVE-2026-77101 Overview

CVE-2026-77101 is a stack-based buffer overflow [CWE-121] in Commvault CommServe that affects service availability. Commvault disclosed the issue in security advisory CV_2026_08_3 and provided a maintenance release to remediate it. The flaw is reachable over the network without authentication or user interaction, and successful exploitation results in a denial-of-service condition against the CommServe service. CommServe is the central management and orchestration component of a Commvault backup deployment, so a disruption directly impacts backup, restore, and data protection workflows across the environment.

Critical Impact
An unauthenticated remote attacker can trigger a stack-based buffer overflow in CommServe to disrupt availability of the central backup and recovery service.

Affected Products

Commvault CommServe (see vendor advisory CV_2026_08_3 for affected version ranges)
Commvault deployments on Microsoft Windows
Commvault deployments on Linux

Discovery Timeline

2026-09-08 - CVE-2026-77101 published to the National Vulnerability Database (NVD)
2026-09-09 - Last updated in the NVD database

Technical Details for CVE-2026-77101

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow in Commvault CommServe. Attacker-supplied input reaches a stack buffer without proper length validation, allowing adjacent stack memory to be overwritten. In this specific case, Commvault characterizes the impact as affecting service availability rather than integrity or confidentiality. That behavior aligns with an overflow that corrupts stack metadata such as return addresses or stack canaries and causes the CommServe process to abort.

Because CommServe is the orchestration authority for a Commvault environment, an outage suspends scheduled backups, restore jobs, and administrative operations. Recovery windows expand until the service is restarted and validated. The issue is reachable over the network and requires no privileges or user interaction, which lowers the barrier for opportunistic exploitation.

Root Cause

The root cause is classified as [CWE-121] Stack-Based Buffer Overflow. A network-facing handler in CommServe copies untrusted input into a fixed-size stack buffer without enforcing a length boundary. When the input exceeds the buffer, adjacent stack frames are corrupted and the process terminates.

Attack Vector

The attack vector is network-based. An unauthenticated attacker sends a crafted request to an exposed CommServe network service to trigger the overflow. Commvault has not published exploit details, and no public proof-of-concept is available at the time of writing. Refer to the Commvault Security Advisory CV_2026_08_3 for vendor-specific technical guidance.

// No verified proof-of-concept is publicly available for CVE-2026-77101.
// Refer to Commvault advisory CV_2026_08_3 for vendor technical details.

Detection Methods for CVE-2026-77101

Indicators of Compromise

Unexpected termination or repeated restarts of the CommServe service process on the management host.
Application or Windows Event Log entries showing access violations, stack corruption, or crash dumps from CommServe binaries.
Failed or missed backup and restore jobs coinciding with CommServe service interruptions.
Inbound network traffic to CommServe management ports from untrusted or unexpected sources.

Detection Strategies

Monitor CommServe process health and generate alerts when the service crashes, restarts, or fails health checks outside maintenance windows.
Correlate crash events with inbound network sessions to CommServe listeners to identify likely exploitation attempts.
Ingest Commvault application logs and Windows or Linux system logs into a centralized analytics platform to hunt for repeated abnormal terminations.

Monitoring Recommendations

Enable crash dump collection on CommServe hosts and forward dumps to a secure analysis location for review.
Track network flow telemetry to CommServe management interfaces and baseline expected client sources.
Alert on gaps in backup job completion telemetry, which often serve as an early signal of CommServe disruption.

How to Mitigate CVE-2026-77101

Immediate Actions Required

Identify all CommServe instances in the environment and confirm their current build against the fixed maintenance release listed in Commvault Security Advisory CV_2026_08_3.
Upgrade affected CommServe deployments to the resolved maintenance release published by Commvault.
Restrict network reachability of CommServe management services to trusted administrative networks only.
Validate backup and restore operations after patching to confirm service integrity.

Patch Information

Commvault has released a maintenance update that resolves the stack-based buffer overflow in CommServe. Customers should apply the fixed maintenance release referenced in Commvault Security Advisory CV_2026_08_3. No workarounds are listed by the vendor as substitutes for the patch.

Workarounds

Enforce network segmentation and firewall rules that limit CommServe access to authorized administrative hosts.
Place CommServe behind a VPN or jump host and block direct exposure to untrusted networks.
Increase monitoring of CommServe process availability until the maintenance release is applied.

bash

# Example: restrict inbound access to CommServe management host using iptables
# Replace <ADMIN_SUBNET> and <COMMSERVE_PORT> with environment-specific values
iptables -A INPUT -p tcp --dport <COMMSERVE_PORT> -s <ADMIN_SUBNET> -j ACCEPT
iptables -A INPUT -p tcp --dport <COMMSERVE_PORT> -j DROP