Commvault QLogin with PublicSharingUser and GUID Password (CVE-2025-57788)

Status: experimental
Severity: medium
Log source: category process_creation, product windows
Author: Swachchhanda Shrawan Poudel (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects a qlogin.exe command attempting to authenticate as the internal _+_PublicSharingUser_ using a GUID as the password. This could be an indicator of an attacker exploiting CVE-2025-57788 to gain initial access using leaked credentials.

Known false positives

Legitimate administrative scripts that use the `_+_PublicSharingUser_` account for valid purposes.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1078.001` Valid Accounts: Default Accounts
Persistence	`T1078.001` Valid Accounts: Default Accounts
Privilege Escalation	`T1078.001` Valid Accounts: Default Accounts
Stealth	`T1078.001` Valid Accounts: Default Accounts

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Commvault QLogin with PublicSharingUser and GUID Password (CVE-2025-57788)
id: 917789e1-2c1f-4bf5-8c91-6f71a017f469
status: experimental
description: |
    Detects a qlogin.exe command attempting to authenticate as the internal `_+_PublicSharingUser_` using a GUID as the password.
    This could be an indicator of an attacker exploiting CVE-2025-57788 to gain initial access using leaked credentials.
references:
    - https://labs.watchtowr.com/guess-who-would-be-stupid-enough-to-rob-the-same-vault-twice-pre-auth-rce-chains-in-commvault/
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-10-20
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.initial-access
    - attack.stealth
    - attack.t1078.001
    - detection.emerging-threats
    - cve.2025-57788
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        CommandLine|contains|all:
            - 'qlogin'
            - '_+_PublicSharingUser_'
        # Detects the use of a GUID as the password, which is indicative of an exploit attempt
        CommandLine|re: '[A-F0-9]{8}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{12}'
    condition: selection
falsepositives:
    - Legitimate administrative scripts that use the `_+_PublicSharingUser_` account for valid purposes.
level: medium

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    CommandLine|contains|all:
        - 'qlogin'
        - '_+_PublicSharingUser_'
    CommandLine|re: '[A-F0-9]{8}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{12}'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`_+_PublicSharingUser_` `qlogin` corpus 2 (sigma 2)	`field:"CommandLine" kind:match`
`CommandLine`	regex_match	`[A-F0-9]{8}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{12}`	`field:"CommandLine" kind:regex_match value:"[A-F0-9]{8}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{4}-[A-F0-9]{12}"`