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How the mentioned CVE works:
Slack Nebula is a scalable overlay networking tool. A flaw exists in versions prior to 1.9.7 where the certificate authority (CA) service incorrectly handles CIDR-based restrictions for node IP address assignment. When validating a certificate signing request (CSR), the CA’s logic for verifying the requested IP address against the predefined allowed CIDR blocks is flawed. This improper validation allows a node to submit a CSR requesting any IP address within the entire Nebula network’s subnet, regardless of the specific CIDR ranges configured for that node’s group or user. Consequently, an authenticated node can bypass intended IP allocation policies and acquire a certificate with an arbitrary source IP, potentially enabling it to impersonate other hosts or intercept traffic within the overlay network.
Platform: Slack Nebula
Version: < 1.9.7
Vulnerability: IP Bypass
Severity: Moderate
date: 2024-10-23
Prediction: Patch 2024-10-30
What Undercode Say:
nebula-cert sign -name attacker -ip 192.168.100.50/24
if !allowedCIDRs.Contains(reqIP) {
return nil
}
How Exploit:
An attacker with a valid Nebula node certificate can craft a malicious Certificate Signing Request (CSR) for an IP address outside their assigned range. By submitting this to the Nebula CA, the flawed validation logic grants the certificate. The attacker then uses this new certificate to join the Nebula network with a spoofed IP, allowing them to communicate with hosts as if they were part of a different, trusted segment.
Protection from this CVE:
Upgrade to Nebula version 1.9.7 or later. This version contains the necessary fixes to the CA’s IP address validation logic, ensuring it correctly enforces the configured CIDR restrictions for all certificate signing requests.
Impact:
The primary impact is a network-level authentication bypass within the Nebula overlay. This can lead to unauthorized access to services intended only for specific IP ranges, potential man-in-the-middle attacks if the spoofed IP is trusted by applications, and a general compromise of network segmentation policies enforced by Nebula.
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Sources:
Reported By: github.com
Extra Source Hub:
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