CVE-2026-49138: Nanobot SSRF in web_fetch Tool—Patch to 0.2.1

Technical summary

The web_fetch tool in Nanobot fails to validate redirect targets before the httpx library processes 3xx Location headers. An authenticated attacker supplies a URL pointing to an external server under their control or a legitimate external host. That server responds with a 3xx redirect (301, 302, etc.) pointing to an internal address such as 127.0.0.1:8080, 192.168.x.x, or 10.0.x.x. Because validation occurs only on the initial URL and not on the resolved endpoint after redirect chain completion, the Nanobot runtime executes the request to the private address. This enables reconnaissance of internal services, potential interaction with backend systems, metadata service endpoints, or other sensitive infrastructure. The vulnerability is classified as CWE-918 (Server-Side Request Forgery).

Business impact

Organizations running Nanobot are exposed to information disclosure from internal networks. Authenticated users—whether legitimate employees or compromised accounts—can enumerate internal services, extract metadata, or trigger unintended interactions with backend systems (databases, cache layers, APIs). In cloud environments, this may include access to instance metadata services that leak credentials or configuration details. While the CVSS score reflects a confined scope and low confidentiality impact, the actual risk depends on what internal infrastructure is reachable from the Nanobot runtime and what data those services expose.

Affected systems

All Nanobot versions prior to 0.2.1 are affected. The vulnerability exists in the web_fetch tool, so any deployment using that functionality is at risk. Verify your installed version and upgrade accordingly. No other vendors or products are implicated in this CVE.

Exploitability

Exploitation requires authentication (CWE-918 in this context is authenticated SSRF), reducing opportunistic attack surface. However, the barrier is moderate: attackers need valid login credentials, which may already be compromised or obtained through phishing. Once authenticated, exploitation is trivial—crafting a malicious redirect chain requires no special tools. The automatic redirect-following behavior of httpx means the attacker does not need to manipulate the Nanobot codebase; they only need to control or predict a URL that will redirect to a private address.

Remediation

Upgrade Nanobot to version 0.2.1 or later. This patch version implements validation of the final resolved URL after all redirects are processed, ensuring that internal or private addresses cannot be reached even if intermediate redirects point to them. Users unable to upgrade immediately should restrict network egress from Nanobot runtimes using firewall rules, blocking outbound access to RFC 1918 private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) and loopback addresses. Limit authentication to Nanobot to trusted users and monitor web_fetch usage patterns for suspicious redirect chains.

Patch guidance

Apply version 0.2.1 or later. Verify with your Nanobot vendor that the patch explicitly disables or validates redirect targets to private/loopback ranges. After patching, test web_fetch functionality with internal URLs to confirm the fix prevents SSRF while maintaining legitimate cross-origin requests. Monitor release notes for any behavioral changes or configuration updates related to redirect handling.

Detection guidance

Monitor Nanobot logs and network traffic for outbound requests originating from Nanobot runtimes to private IP ranges or loopback addresses. Flag HTTP 3xx responses in web_fetch requests that originate from external or user-controlled domains, particularly if followed by a request to an internal address. Inspect authentication logs for unusual login activity followed by web_fetch operations. Network-side, use IDS/IPS rules to detect SSRF patterns: external-to-internal requests with high entropy in the referring URL parameter. Consider deploying endpoint detection on systems hosting Nanobot to capture process-level egress to private networks.

Why prioritize this

While the CVSS score is MEDIUM (5.0) and the vulnerability requires authentication, it merits priority patching because it enables lateral movement and reconnaissance in segmented networks. Authenticated SSRF is a significant chaining risk—once an attacker gains initial access, they leverage this flaw to map internal infrastructure and locate high-value targets. In cloud environments, instance metadata access is a known privilege escalation vector. Organizations with strict network segmentation and strong authentication posture face lower immediate risk, but those with shared or contractor access to Nanobot should treat this as high priority. The fix is straightforward and low-risk, making swift deployment advisable.

Risk score, explained

The CVSS 3.1 score of 5.0 (MEDIUM) reflects: Attack Vector = Network (remote exploitation possible), Attack Complexity = Low (redirect behavior is automatic), Privileges Required = Low (authentication necessary but not admin), User Interaction = None (no social engineering needed post-authentication), Scope = Changed (attacker can reach systems outside the original authorization boundary), Confidentiality = Low (information disclosure from internal services), Integrity = None, Availability = None. The score appropriately penalizes SSRF but does not fully capture lateral movement or metadata service abuse risks, which are context-dependent. Use this score as a baseline; adjust local priority based on your network topology and the sensitivity of internal services reachable from Nanobot.

Frequently asked questions