CVE-2026-41272 Overview
CVE-2026-41272 is a Server-Side Request Forgery (SSRF) vulnerability in Flowise, a drag & drop user interface for building customized large language model flows. Prior to version 3.1.0, the core security wrappers (secureAxiosRequest and secureFetch) intended to prevent SSRF attacks contain multiple logic flaws. These flaws allow attackers to bypass allow/deny lists via DNS Rebinding (Time-of-Check Time-of-Use) or by exploiting the default configuration which fails to enforce any deny list.
Critical Impact
Attackers can bypass SSRF protections to access internal network resources, potentially leading to unauthorized data access, internal service enumeration, and lateral movement within protected networks.
Affected Products
- Flowise versions prior to 3.1.0
Discovery Timeline
- 2026-04-23 - CVE CVE-2026-41272 published to NVD
- 2026-04-23 - Last updated in NVD database
Technical Details for CVE-2026-41272
Vulnerability Analysis
This vulnerability (CWE-918) affects the security wrapper functions in Flowise that are designed to prevent Server-Side Request Forgery attacks. The secureAxiosRequest and secureFetch functions contain fundamental logic flaws that undermine their protective capabilities.
The first flaw involves a Time-of-Check Time-of-Use (TOCTOU) race condition that enables DNS Rebinding attacks. When Flowise validates a URL, it resolves the hostname to an IP address and checks it against allow/deny lists. However, an attacker can configure a malicious DNS server to return a legitimate external IP during the initial check, then rapidly change the DNS response to an internal IP address (such as 127.0.0.1 or 192.168.x.x) by the time the actual request is made.
The second flaw is equally critical: the default configuration fails to enforce any deny list, meaning fresh installations or deployments without explicit configuration offer no protection against SSRF attacks targeting internal infrastructure.
Root Cause
The root cause stems from two distinct issues in the security wrapper implementation. First, the validation logic performs DNS resolution separately from the actual HTTP request, creating a timing window for DNS Rebinding attacks. Second, the deny list enforcement requires explicit configuration and does not ship with sensible defaults that block common internal IP ranges (RFC 1918 addresses, localhost, link-local addresses).
Attack Vector
An attacker with low-privilege access to a Flowise instance can exploit this vulnerability over the network. The attack requires crafting malicious URLs that either point to attacker-controlled DNS servers configured for rebinding, or simply target internal resources directly in default-configured installations. This can enable access to internal services, cloud metadata endpoints (such as 169.254.169.254), or other sensitive network resources that should be inaccessible from the Flowise application.
Detection Methods for CVE-2026-41272
Indicators of Compromise
- Unusual outbound DNS queries with very short TTL values indicating potential DNS Rebinding setup
- HTTP requests from Flowise servers targeting internal IP ranges (127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
- Requests to cloud metadata endpoints such as 169.254.169.254
- Multiple rapid DNS resolutions for the same hostname with different IP addresses
Detection Strategies
- Monitor network traffic from Flowise instances for connections to internal IP ranges or metadata services
- Implement DNS monitoring to detect suspicious rebinding patterns with rapidly changing A records
- Review Flowise application logs for requests to unexpected internal endpoints
- Deploy network segmentation monitoring to detect unauthorized east-west traffic originating from Flowise
Monitoring Recommendations
- Configure alerting for any Flowise outbound connections to RFC 1918 private address spaces
- Enable DNS query logging on internal resolvers to track resolution patterns from Flowise hosts
- Implement egress filtering rules with logging to capture attempted SSRF exploitation
- Monitor for HTTP requests to well-known metadata service IPs across cloud environments
How to Mitigate CVE-2026-41272
Immediate Actions Required
- Upgrade Flowise to version 3.1.0 or later immediately
- Review Flowise configuration to ensure explicit deny lists are configured for internal IP ranges
- Implement network-level controls to prevent Flowise from accessing internal resources
- Audit logs for signs of previous exploitation attempts targeting internal services
Patch Information
This vulnerability is fixed in Flowise version 3.1.0. The patch addresses both the DNS Rebinding vulnerability and the default configuration issue. For more details, refer to the GitHub Security Advisory.
Workarounds
- Configure explicit deny lists blocking all RFC 1918 ranges, localhost, and cloud metadata IPs in Flowise settings
- Deploy network-level firewall rules restricting Flowise server egress to only required external services
- Use a forward proxy with strict allow-listing for outbound HTTP requests from Flowise
- Implement DNS pinning at the infrastructure level to mitigate DNS Rebinding attacks
# Example network-level mitigation using iptables
# Block Flowise server from accessing internal networks
iptables -A OUTPUT -m owner --uid-owner flowise -d 10.0.0.0/8 -j DROP
iptables -A OUTPUT -m owner --uid-owner flowise -d 172.16.0.0/12 -j DROP
iptables -A OUTPUT -m owner --uid-owner flowise -d 192.168.0.0/16 -j DROP
iptables -A OUTPUT -m owner --uid-owner flowise -d 127.0.0.0/8 -j DROP
iptables -A OUTPUT -m owner --uid-owner flowise -d 169.254.169.254/32 -j DROP
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