Adversaries may exfiltrate data to a webhook endpoint rather than over their primary command and control channel. Webhooks are simple mechanisms for allowing a server to push data over HTTP/S to a client without the need for the client to continuously poll the server.(Citation: RedHat Webhooks) Many public and commercial services, such as Discord, Slack, and `webhook.site`, support the creation of webhook endpoints that can be used by other services, such as Github, Jira, or Trello.(Citation: Discord Intro to Webhooks) When changes happen in the linked services (such as pushing a repository update or modifying a ticket), these services will automatically post the data to the webhook endpoint for use by the consuming application. 

Adversaries may link an adversary-owned environment to a victim-owned SaaS service to achieve repeated [Automated Exfiltration](https://attack.mitre.org/techniques/T1020) of emails, chat messages, and other data.(Citation: Push Security SaaS Attacks Repository Webhooks) Alternatively, instead of linking the webhook endpoint to a service, an adversary can manually post staged data directly to the URL in order to exfiltrate it.(Citation: Microsoft SQL Server)

Access to webhook endpoints is often over HTTPS, which gives the adversary an additional level of protection. Exfiltration leveraging webhooks can also blend in with normal network traffic if the webhook endpoint points to a commonly used SaaS application or collaboration service.(Citation: CyberArk Labs Discord)(Citation: Talos Discord Webhook Abuse)(Citation: Checkmarx Webhooks)
Exfiltration Over Webhook
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1567/004  external_id: T1567.004     source_name: Checkmarx Webhooks  description:  Jossef Harush Kadouri. (2022, March 7). Webhook Party — Malicious packages caught exfiltrating data via legit webhook services. Retrieved July 20, 2023.  url: https://medium.com/checkmarx-security/webhook-party-malicious-packages-caught-exfiltrating-data-via-legit-webhook-services-6e046b07d191     source_name: CyberArk Labs Discord  description: CyberArk Labs. (2023, April 13). The (Not so) Secret War on Discord. Retrieved July 20, 2023.  url: https://www.cyberark.com/resources/threat-research-blog/the-not-so-secret-war-on-discord     source_name: Discord Intro to Webhooks  description: D. (n.d.). Intro to Webhooks. Retrieved July 20, 2023.  url: https://support.discord.com/hc/en-us/articles/228383668-Intro-to-Webhooks     source_name: Microsoft SQL Server  description: Microsoft Threat Intelligence. (2023, October 3). Defending new vectors: Threat actors attempt SQL Server to cloud lateral movement. Retrieved October 3, 2023.  url: https://www.microsoft.com/security/blog/2023/10/03/defending-new-vectors-threat-actors-attempt-sql-server-to-cloud-lateral-movement/     source_name: Talos Discord Webhook Abuse  description: Nick Biasini, Edmund Brumaghin, Chris Neal, and Paul Eubanks. (2021, April 7). https://blog.talosintelligence.com/collab-app-abuse/. Retrieved July 20, 2023.  url: https://blog.talosintelligence.com/collab-app-abuse/     source_name: Push Security SaaS Attacks Repository Webhooks  description: Push Security. (2023, July 31). Webhooks. Retrieved August 4, 2023.  url: https://github.com/pushsecurity/saas-attacks/blob/main/techniques/webhooks/description.md     source_name: RedHat Webhooks  description: RedHat. (2022, June 1). What is a webhook?. Retrieved July 20, 2023.  url: https://www.redhat.com/en/topics/automation/what-is-a-webhook     