Domain restrictions bypass via DNS Rebinding in WireMock and WireMock Studio webhooks, proxy and recorder modes

Impact

The proxy mode of WireMock, can be protected by the network restrictions configuration, as documented in Preventing proxying to and recording from specific target addresses. These restrictions can be configured using the domain names, and in such a case the configuration is vulnerable to the DNS rebinding attacks. A similar patch was applied in WireMock 3.0.0-beta-15 for the WireMock Webhook Extensions.

The root cause of the attack is a defect in the logic which allows for a race condition triggered by a DNS server whose address expires in between the initial validation and the outbound network request that might go to a domain that was supposed to be prohibited. Control over a DNS service is required to exploit this attack, so it has high execution complexity and limited impact.

Affected versions

• WireMock 3,x until 3.0.3 (security patch), on default settings in environments with access to the network
• WireMock 2.x until 2.35.1 (security patch), on default settings in environments with access to the network
• Python WireMock until 2.6.1
• WireMock Studio - all versions, this proprietary product was discontinued in 2022

Patches

• WireMock 3.0.3 + the 3.0.3-1 Docker image
• WireMock 2.35.1 + the 2.35.1-1 Docker image - backport to WireMock 2.x
• Python WireMock 2.6.1

Workarounds

For WireMock:

• Option 1: Configure WireMock to use IP addresses instead of the domain names in the outbound URLs subject to DNS rebinding
• Option 2: Use external firewall rules to define the list of permitted destinations

For WireMock Studio: N/A. Switch to another distribution, there will be no fix provided. The vendor of former WireMock Studio recommends migration to WireMock Cloud

References

• CVE-2023-41327 - Related issue in the WireMock Webhooks Extension