Ollama Windows updater flaws enable silent RCE

Two chained flaws in Ollama for Windows let attackers bypass update signature checks and path-traverse malicious payloads into the Startup folder for silent, automatic code execution.

CERT Polska coordinated disclosure of two vulnerabilities affecting Ollama for Windows' auto-update mechanism. CVE-2026-42248 shows that, unlike other platforms, the Windows update verification routine unconditionally returns success, meaning no digital signature or trust validation is performed before staging or executing update payloads. CVE-2026-42249 is a path traversal RCE where attacker-controlled HTTP response headers are used to construct local file paths via filepath.Join without sanitization, allowing writes outside the intended staging directory—including into the Windows Startup folder.

When chained, an attacker capable of influencing update responses (e.g., via a man-in-the-middle or compromised update channel) can deliver a malicious executable that is written to a persistence location and silently executed without any user interaction, since Ollama for Windows performs automatic updates by default. This results in automatic, persistent code execution without user awareness.

Versions 0.12.10 through 0.17.5 were confirmed vulnerable during testing; other versions were untested but may also be affected. The maintainers were notified early but did not respond with vulnerability details or a confirmed affected version range, leaving the full scope of impact unclear. No patch status or exploitation-in-the-wild evidence is mentioned in the report.

title: Ollama Process Writing to Windows Startup Folder
description: Detects Ollama or related processes (ollama.exe, update utilities) writing
  .exe or .cmd files to Windows Startup folders. CVE-2026-42249 path traversal allows
  update payloads to be staged in persistence locations.
tags:
- attack.persistence
- attack.t1547.001
logsource:
  category: file_event
  product: windows
detection:
  selection:
    Image|endswith:
    - \ollama.exe
    - \ollama-launcher.exe
    TargetFilename|contains:
    - \AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\
    - \ProgramData\Microsoft\Windows\Start Menu\Programs\Startup\
    TargetFilename|endswith:
    - .exe
    - .cmd
    - .bat
    - .vbs
    - .ps1
  condition: selection
falsepositives:
- Legitimate Ollama installer adding uninstaller shortcuts to Startup folder
level: high
id: c44bac98-5759-588b-8455-e5ca235d3209
status: experimental
author: Vorant

title: Ollama Update Process Loading Without Code Signature Validation
description: Detects Ollama update-related processes (ollama.exe, ollama-update, update
  utilities) spawning child processes from the update staging directory without preceding
  signature validation events. CVE-2026-42248 bypasses signature checks on Windows.
tags:
- attack.defense-evasion
- attack.t1553.002
logsource:
  category: process_creation
  product: windows
detection:
  selection_ollama_child:
    ParentImage|endswith:
    - \ollama.exe
    - \ollama-launcher.exe
    - \ollama-update.exe
    Image|endswith: .exe
    CommandLine|contains:
    - \AppData\Local
    - \Temp\
    - \ProgramData\
  filter_signed_paths:
    Image|startswith:
    - C:\Program Files
    - C:\Program Files (x86)\
    - C:\Windows\System32\
  condition: selection_ollama_child and not filter_signed_paths
falsepositives:
- Ollama legitimately launching helper utilities from its staging directory
level: medium
id: d9072ab6-a948-51cc-8c87-ad4493bc4220
status: experimental
author: Vorant

title: Ollama Update Mechanism Enumerating or Writing to System Directories
description: Detects Ollama-related processes (ollama.exe, update utilities) writing
  files to Windows system startup, temp, or local application data directories without
  a legitimate staging subdirectory, indicating potential path traversal abuse.
tags:
- attack.discovery
- attack.t1083
logsource:
  category: file_event
  product: windows
detection:
  selection_write:
    Image|endswith:
    - \ollama.exe
    - \ollama-update.exe
    - \ollama-launcher.exe
    TargetFilename|contains:
    - \AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup
    - \ProgramData\Microsoft\Windows\Start Menu\Programs\Startup
    - \AppData\Local\Temp\
    EventType: SetFileCreateTime
  filter_expected_temp:
    TargetFilename|contains: \AppData\Local\Temp\ollama
  condition: selection_write and not filter_expected_temp
falsepositives:
- Ollama cleanup processes removing old update artifacts from temp directories
level: high
id: 27644b5a-c974-5e9f-9e44-d91a3b18fb53
status: experimental
author: Vorant

Source reporting: https://cert.pl/en/posts/2026/04/CVE-2026-42248