# SP-019 Secure Ad-Hoc File Exchange Pattern

Status: published. Release 26.02. Modified 2026-02-06. Licence: CC BY-SA 4.0.

Scope: Security architecture for enabling secure, business-driven file sharing with external partners without pre-established federation. Covers encrypted file transfer, access control for external recipients, audit trails, strong authentication, boundary protection, and the balance between usability and data protection in ad-hoc collaboration scenarios.
Use when: The pattern is best suited when the following indicators are present: the business drives ad-hoc decisions about when and where the solution is needed; a simplified user interface is required that allows staff with low IT affinity to use the solution; low integration costs are desired; identity federation with the external partner is not established; the business unit is the data owner and staff members decide who...
Not when: Strong integration into a document management workflow that requires a single repository for internal and external collaboration -- in this case, a unified collaboration platform (SharePoint Online, Box, Google Workspace) with external sharing controls is more appropriate.

## Controls (25, NIST SP 800-53 ids)
- Critical (5): AC-02, AU-04, SC-07, SC-09, SC-13
- Important (9): AC-07, AC-20, AT-02, AU-06, CA-02, CA-03, IA-04, RA-03, RA-05
- Standard (11): AC-10, AC-12, AT-03, AT-05, CM-03, CP-02, CP-09, IR-04, IR-07, MA-02, MA-06
- Withdrawn from SP 800-53 by NIST: AT-05 (now in PM-15); SC-09 (now in SC-08)

## What each critical control mitigates (5)
- AC-02 Account Management: T-FX-001, T-FX-007, T-FX-008
- AU-04 Audit Log Storage Capacity: T-FX-007, T-FX-009
- SC-07 Boundary Protection: T-FX-002, T-FX-005
- SC-09 Transmission Confidentiality: T-FX-002
- SC-13 Cryptographic Protection: T-FX-001, T-FX-002, T-FX-006

## Threats and the controls that mitigate them (10)
- T-FX-001 Unauthorised File Access via Credential Compromise: AC-02, AC-07, SC-13, RA-05
- T-FX-002 Data Interception During File Transfer: SC-09, SC-13, SC-07
- T-FX-003 Bypass of Secure Exchange via Shadow IT Channels: AT-02, AT-03, AC-20
- T-FX-004 Brute-Force Attack on Exchange Authentication: AC-07, AC-10, AC-12, AU-06
- T-FX-005 Malware Delivery via Uploaded Files: SC-07, RA-05, IR-04
- T-FX-006 Platform Compromise Leading to Bulk Data Exposure: RA-05, CM-03, SC-13, CA-02
- T-FX-007 Insider Abuse of File Exchange Capabilities: AU-04, AU-06, AC-02, AT-02
- T-FX-008 Data Persistence Beyond Retention Period: AC-02, CP-09, MA-02
- T-FX-009 Loss of Audit Trail Integrity: AU-04, AU-06, CP-09
- T-FX-010 Service Unavailability During Critical Business Exchange: CP-02, MA-02, MA-06, IR-07

## More
- The critical controls and what each mitigates, as JSON (a few KB): /api/v1/patterns/SP-019/crosswalk?emphasis=critical
- The same for every control, with its clauses in a framework: /api/v1/patterns/SP-019/crosswalk?framework={framework id}. Framework ids are listed in /llms.txt
- The pattern's prose, examples and references as JSON, 24 KB: /api/v1/patterns/SP-019
- Page for people: /patterns/sp-019/
- Found an error? Open an issue at https://github.com/opensecurityarchitecture/osa-data/issues with the id, what OSA says and what the source says.
- Related: SP-013 Data Security Pattern; SP-016 DMZ Module; SP-014 Awareness and Training Pattern; SP-010 Identity Management Pattern; SP-018 Information Security Management System

This card, the API and the page are generated from one file. Checking one against another adds no evidence.