CVE-2026-77100: MediaAgent Heap Buffer Overflow Vulnerability

CVE-2026-77100 Overview

CVE-2026-77100 is a heap-based buffer overflow in Commvault MediaAgent that affects service availability. The flaw is categorized under [CWE-122] and can be triggered remotely over the network without authentication or user interaction. Successful exploitation causes a denial of service against the MediaAgent, disrupting backup and recovery operations. The vulnerability also impacts HyperScale appliances that run MediaAgent components. Commvault has published advisory CV_2026_10_6 and recommends upgrading affected installations to a resolved maintenance release.

Critical Impact
An unauthenticated remote attacker can corrupt heap memory in MediaAgent and crash the backup service, interrupting data protection operations across Commvault and HyperScale deployments.

Affected Products

Commvault MediaAgent
Commvault HyperScale
Commvault installations deploying MediaAgent components

Discovery Timeline

2026-10-13 - CVE-2026-77100 published to NVD
2026-10-14 - Last updated in NVD database

Technical Details for CVE-2026-77100

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow [CWE-122] in the Commvault MediaAgent service. MediaAgent handles data movement between clients and storage targets, exposing network listeners used by other Commvault components. An attacker who sends crafted input to a reachable MediaAgent service can write past the bounds of a heap-allocated buffer. The resulting memory corruption terminates the MediaAgent process and halts backup, restore, and auxiliary copy jobs that depend on it.

The CVSS vector indicates the vulnerability impacts availability only. Confidentiality and integrity remain unaffected, which is consistent with a service crash rather than code execution or data exposure. The EPSS probability currently sits at 0.316% (percentile 22.9), reflecting no observed in-the-wild exploitation at this time.

Root Cause

The root cause is improper validation of input length or structure before copying data into a heap-allocated buffer within MediaAgent. When the input exceeds the allocated size, adjacent heap metadata and objects are overwritten, leading to process termination. Commvault's advisory CV_2026_10_6 identifies the condition as a heap-based buffer overflow affecting service availability.

Attack Vector

The attack vector is Network with low attack complexity, no privileges, and no user interaction. An attacker with network reachability to a MediaAgent listener can deliver a malformed payload to trigger the overflow. Environments exposing MediaAgent services beyond trusted management networks increase the exposure window. Refer to the Commvault Security Advisory CV_2026_10_6 for additional technical context.

Detection Methods for CVE-2026-77100

Indicators of Compromise

Unexpected MediaAgent service crashes or restarts logged by the Commvault services supervisor.
Backup, restore, or auxiliary copy jobs failing with abrupt connection termination to a MediaAgent.
Core dumps or Windows Error Reporting entries referencing MediaAgent binaries on affected hosts.

Detection Strategies

Monitor MediaAgent process lifecycle events and alert on repeated abnormal terminations across backup infrastructure.
Inspect network traffic to MediaAgent listening ports for malformed or oversized protocol messages originating from unexpected sources.
Correlate job failure spikes in the CommCell with host-level crash telemetry to surface exploitation attempts.

Monitoring Recommendations

Forward Commvault event logs and host crash telemetry to the SIEM for centralized correlation.
Baseline the set of clients that normally communicate with each MediaAgent and alert on new or external sources.
Track patch state of all MediaAgent and HyperScale nodes and alert when an unpatched node receives external traffic.

How to Mitigate CVE-2026-77100

Immediate Actions Required

Inventory all MediaAgent and HyperScale nodes and identify versions exposed to CVE-2026-77100.
Restrict network reachability of MediaAgent services to trusted CommCell components using firewall rules.
Apply the resolved maintenance release from Commvault as soon as change windows allow.

Patch Information

Commvault directs customers to upgrade affected MediaAgent and HyperScale installations to the resolved maintenance release identified in advisory CV_2026_10_6. Full remediation details are available in the Commvault Security Advisory CV_2026_10_6.

Workarounds

Limit MediaAgent service exposure to the management VLAN and block ingress from untrusted networks.
Enforce network segmentation between backup infrastructure and general user or internet-facing segments.
Monitor MediaAgent service health and automate restart with alerting until patches are deployed.

bash

# Example firewall restriction limiting MediaAgent access to trusted CommServe hosts
iptables -A INPUT -p tcp --dport 8400:8403 -s <trusted_commserve_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 8400:8403 -j DROP