CVE-2026-21791: HCL Sametime Information Disclosure Flaw

CVE-2026-21791 Overview

CVE-2026-21791 affects HCL Sametime for Android, where the application writes hostname information into application logs and certain URLs. This behavior exposes infrastructure details to any local actor or co-resident application able to read those logs. The flaw is classified under [CWE-532] (Insertion of Sensitive Information into Log File) and requires local access with low privileges to exploit. No user interaction is needed, and the impact is limited to confidentiality of logged data.

Critical Impact
Local actors with access to Android log output can harvest internal hostnames embedded in Sametime application logs, aiding reconnaissance against enterprise collaboration infrastructure.

Affected Products

HCL Sametime for Android (mobile client)
Vendor: HCL Technologies (hcltech:sametime)
Platform: Android

Discovery Timeline

2026-03-10 - CVE-2026-21791 published to the National Vulnerability Database
2026-05-07 - Last updated in NVD database

Technical Details for CVE-2026-21791

Vulnerability Analysis

The vulnerability is an information disclosure issue in the Android build of HCL Sametime. The client logs hostname strings during normal operation and embeds hostnames in certain URLs that are recorded by the application. These artifacts persist in Android log buffers and any file-based log destinations the app writes to. An attacker with local access to the device, or another application with permission to read shared log output, can extract this data.

The issue maps to [CWE-532], where sensitive information is written to log files that are accessible beyond the trust boundary of the application that produced them. Disclosed hostnames can reveal internal server naming conventions, on-premises Sametime deployment topology, and reverse-proxy or gateway fully qualified domain names (FQDNs). This information supports targeted phishing, lateral movement planning, and external reconnaissance against the enterprise messaging backbone.

The CVSS vector indicates a local attack vector, low complexity, low privileges required, no user interaction, and a confidentiality-only impact. Neither integrity nor availability is affected. The EPSS probability is 0.015%, reflecting low likelihood of opportunistic exploitation in the wild.

Root Cause

The root cause is improper handling of diagnostic logging. Developers included hostname values in log statements and URL trace records without sanitization or redaction. Android applications that emit verbose log data risk exposing that data to other processes, debugging tools, or backup archives.

Attack Vector

Exploitation requires local access to the Android device or to artifacts derived from it, such as bug reports, ADB log captures, or device backups. An attacker reads the application logs and parses hostname strings or URL paths. No network access to the Sametime infrastructure is required to obtain the disclosed values. Refer to the HCL Software Knowledge Base Article for vendor-specific exploitation context.

Detection Methods for CVE-2026-21791

Indicators of Compromise

Presence of internal hostname strings or FQDNs in Android logcat output from the Sametime process
Sametime application log files containing URLs that embed backend server names
Unexpected access to device bug reports, log archives, or adb logcat sessions on managed devices

Detection Strategies

Inspect Sametime-generated logs on managed Android devices for hostname patterns matching internal infrastructure
Use mobile device management (MDM) to flag installations of Sametime versions predating the vendor fix
Correlate access to Android debug bridge or developer mode toggling with the presence of Sametime on the same device

Monitoring Recommendations

Monitor MDM telemetry for sideloaded log-reader utilities or unauthorized debug-tool activity on devices running Sametime
Track outbound DNS or HTTP requests to internal hostnames originating from unmanaged endpoints, which may indicate prior reconnaissance using disclosed FQDNs
Audit enterprise file-sharing locations for uploaded Android bug reports or log bundles that may contain Sametime entries

How to Mitigate CVE-2026-21791

Immediate Actions Required

Upgrade HCL Sametime for Android to the fixed release identified in the HCL Software Knowledge Base Article
Restrict installation of Sametime to managed devices enrolled in MDM with logging and developer options disabled
Purge existing local log artifacts and bug reports that may contain hostname disclosures

Patch Information

HCL has published remediation guidance through its support portal. Review the HCL Software Knowledge Base Article for the fixed version and upgrade instructions specific to the Android client.

Workarounds

Disable verbose or diagnostic logging in the Sametime Android client where the option is exposed
Enforce MDM policy that blocks USB debugging and restricts the READ_LOGS permission on managed Android devices
Limit Sametime usage to corporate-managed devices, preventing log extraction on personal endpoints

bash

# Configuration example: Android MDM policy snippet to restrict debugging and log access
adb shell settings put global development_settings_enabled 0
adb shell settings put global adb_enabled 0
# Enforce via MDM: deny android.permission.READ_LOGS to non-system apps
# Enforce via MDM: disable USB debugging and bug report sharing