CVE-2026-64873 Overview
CVE-2026-64873 is a Server-Side Request Forgery (SSRF) vulnerability [CWE-918] affecting Regular Labs software. The flaw allows custom query URLs to reach internal or reserved network services that should be inaccessible from external clients. Attackers can abuse this behavior to probe internal infrastructure, bypass network segmentation, and interact with services listening on private address ranges. The vulnerability was published to the National Vulnerability Database on July 23, 2026. Vendor severity, CVSS scoring, and specific affected versions have not been assigned in the public advisory at the time of publication.
Critical Impact
Attackers can craft custom query URLs to force the application to send requests to internal or reserved network addresses, enabling reconnaissance and interaction with internal services.
Affected Products
- Regular Labs software (specific product and version details not provided in the advisory)
- Extensions relying on the vulnerable custom query URL handler
- Deployments exposing the affected feature to untrusted users
Discovery Timeline
- 2026-07-23 - CVE-2026-64873 published to NVD
- 2026-07-23 - Last updated in NVD database
Technical Details for CVE-2026-64873
Vulnerability Analysis
The vulnerability is a Server-Side Request Forgery (SSRF) issue classified under [CWE-918]. The affected component accepts user-controlled URLs as part of a custom query feature. The application then issues server-side HTTP requests to those URLs without adequate validation of the destination. Because the request originates from the server, it can reach hosts and ports that are unreachable from the public internet, including loopback interfaces, RFC 1918 private ranges, link-local addresses, and cloud metadata endpoints.
An attacker supplying a crafted URL can enumerate internal services, retrieve responses from those services, or trigger side effects on unauthenticated internal APIs. Cloud deployments face additional risk because metadata services frequently return temporary credentials to any local requester.
Root Cause
The root cause is missing or insufficient validation of destination hosts in the custom query URL handler. The code does not filter loopback, private, link-local, or reserved IP ranges before dispatching an outbound HTTP request. DNS rebinding and IP encoding tricks may further complicate any incomplete allowlist logic.
Attack Vector
An attacker submits a custom query URL pointing to an internal resource, for example a metadata endpoint or an internal administrative interface. The server fetches the target and may return response contents, headers, or timing signals to the attacker. Repeated requests allow port scanning and service fingerprinting of the internal network.
No verified exploit code has been published. Refer to the Regular Labs Security Page for vendor guidance.
Detection Methods for CVE-2026-64873
Indicators of Compromise
- Outbound HTTP requests from the application server to RFC 1918 addresses, 127.0.0.0/8, or 169.254.169.254
- Unexpected access log entries containing user-supplied URLs pointing to internal hostnames or IP literals
- Spikes in server-initiated connections to non-standard internal ports indicative of port scanning
Detection Strategies
- Inspect application logs for custom query URL parameters that resolve to internal or reserved IP ranges
- Correlate web request logs with egress firewall logs to identify server-originated traffic to private networks
- Alert on any application-layer request whose destination host is a cloud metadata endpoint
Monitoring Recommendations
- Enable egress traffic monitoring on the application host and forward logs to a centralized analytics platform
- Baseline normal outbound destinations for the application and alert on deviations to internal ranges
- Monitor for repeated request patterns to sequential internal IPs or ports, indicating scanning behavior
How to Mitigate CVE-2026-64873
Immediate Actions Required
- Restrict access to the custom query URL feature to authenticated administrators only
- Block server-initiated egress traffic to internal, loopback, and cloud metadata address ranges at the network layer
- Review recent application logs for suspicious custom query URLs referencing internal hosts
Patch Information
Consult the Regular Labs Security Page for the vendor patch and updated version details. Apply the vendor-supplied update as soon as it becomes available for your deployment.
Workarounds
- Disable the custom query URL feature if it is not required for business operations
- Enforce an allowlist of permitted destination hosts for outbound requests originating from the application
- Require IMDSv2 with hop-limit restrictions on AWS instances to prevent metadata credential theft via SSRF
# Example egress restriction using iptables to block SSRF to internal ranges
iptables -A OUTPUT -m owner --uid-owner www-data -d 127.0.0.0/8 -j REJECT
iptables -A OUTPUT -m owner --uid-owner www-data -d 10.0.0.0/8 -j REJECT
iptables -A OUTPUT -m owner --uid-owner www-data -d 172.16.0.0/12 -j REJECT
iptables -A OUTPUT -m owner --uid-owner www-data -d 192.168.0.0/16 -j REJECT
iptables -A OUTPUT -m owner --uid-owner www-data -d 169.254.0.0/16 -j REJECT
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
