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How CVE-2026-53945 Works
Ghost is a Node.js-based content management system. Starting from version 6.0.9, it included a private-IP check mechanism designed to prevent the server from making outbound HTTP requests to internal network addresses. This security control is critical to mitigate Server-Side Request Forgery (SSRF) attacks, which could otherwise allow an attacker to coerce the server into interacting with internal services, such as cloud metadata endpoints (e.g., 169.254.169.254), internal APIs, or other hosts on the local network.
The vulnerability arises from a Time-of-Check to Time-of-Use (TOCTOU) race condition, classified under CWE-367. The flawed logic performs a security check on the IP address resolved from a domain name at the moment the request is initiated. However, due to the asynchronous nature of DNS resolution and the underlying network stack, an attacker can exploit DNS rebinding to subvert this check.
In a DNS rebinding attack, the attacker controls a malicious domain. When the Ghost server first resolves this domain to perform the private-IP check, the DNS server returns a benign public IP address, which passes the validation. Immediately after the check passes, the attacker changes the DNS response for the same domain to resolve to an internal IP address (e.g., 192.168.1.1 or 169.254.169.254). Because the HTTP request’s socket connection is established after the validation step, it uses the second, malicious IP address, thus bypassing the security control. This allows the Ghost server to be coerced into making requests to internal network hosts through features that perform external fetches, such as oEmbed, webmentions, and recommendations.
The vulnerability affects all self-hosted Ghost instances from version 6.0.9 up to and including 6.21.0. It is fixed in version 6.21.1. The vulnerability is classified as Medium severity with a CVSS v3.1 base score of 4.0.
DailyCVE Form
Platform: ……. Ghost CMS
Version: …….. 6.0.9 to 6.21.0
Vulnerability :…… SSRF via DNS Rebinding (CWE-367)
Severity: ……. Medium (CVSS 4.0)
date: ………. June 24, 2026
Prediction: ……. Already Patched (v6.21.1)
What Undercode Say: Analytics
The fix for CVE-2026-53945 was implemented in commit 07d6041. The patch addresses the root cause by injecting a custom `options.lookup` function into the native HTTP configuration for outbound requests. This ensures that the DNS resolution used for the security check is the same as the one used for establishing the socket connection, effectively eliminating the TOCTOU race condition.
– Vulnerable Code Pattern: The original logic performed IP validation after DNS resolution but before the socket was created, leaving a window for DNS rebinding.
– Fixed Code Pattern: The patch synchronizes the DNS lookup and connection establishment, ensuring that the IP address validated is the one actually connected to.
– Affected Features: The vulnerability can be triggered through any feature that issues outbound HTTP requests, including:
– oEmbed
– Webmentions
– Recommendations
Bash Commands for Analysis:
Check current Ghost version ghost version Or check the version in your Ghost installation directory cd /path/to/ghost npm list ghost --depth=0 Check for the vulnerable commit range git log --oneline --grep="07d6041"
Exploit
An attacker can exploit this vulnerability by following these steps:
1. Setup: The attacker registers a domain (e.g., attacker.com) and configures a DNS server with a very low TTL (Time-To-Live).
2. Initial Request: The attacker crafts a request to a vulnerable Ghost endpoint (e.g., an oEmbed endpoint) that triggers an outbound fetch to attacker.com.
3. First DNS Response: The Ghost server performs a DNS lookup for attacker.com. The attacker’s DNS server responds with a public IP address (e.g., 1.2.3.4), which passes the private-IP check.
4. Rebinding: After the check passes, the attacker changes the DNS record for `attacker.com` to resolve to an internal IP address (e.g., `192.168.1.1` or 169.254.169.254).
5. Second DNS Response: The Ghost server proceeds to establish the HTTP connection. It performs another DNS lookup for `attacker.com` and receives the internal IP address.
6. SSRF: The Ghost server then makes an HTTP request to the internal IP address, potentially accessing sensitive internal services.
PoC Concept (Conceptual):
Example of triggering an outbound fetch via oEmbed curl -X GET "https://vulnerable-ghost.com/api/oembed?url=http://attacker.com/some-content"
Protection
- Upgrade to version 6.21.1 or later: This is the primary and most effective mitigation.
– For Docker-based installations: Pull the latest official Ghost Docker image.
– For Ghost-CLI installations: Run ghost update.
2. Network Egress Filtering: If an immediate upgrade is not possible, implement egress firewall rules to block the Ghost server from initiating connections to internal IP ranges. This includes blocking:
– RFC 1918 networks (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
– Loopback (127.0.0.0/8)
– Link-local (169.254.0.0/16)
– Cloud metadata endpoints (e.g., 169.254.169.254)
Example iptables rule to block access to metadata endpoint iptables -A OUTPUT -d 169.254.169.254 -j DROP
3. Disable Vulnerable Features: Temporarily disable features that trigger outbound fetches, such as oEmbed, webmentions, and recommendations. This reduces the attack surface but does not fix the underlying vulnerability.
4. Set NODE_ENV to production: Ensure production deployments have `NODE_ENV` set to production. This can help mitigate some development-specific risks but is not a direct fix for this vulnerability.
Impact
- Unauthorized Internal Network Access: An attacker can force the Ghost server to make HTTP requests to internal hosts, including databases, internal APIs, and cloud metadata services.
- Information Disclosure: The attacker may be able to read sensitive information from internal services, such as cloud instance metadata (including AWS credentials, IAM roles, etc.).
- Limited Integrity Impact: The CVSS vector indicates a low integrity impact, meaning the attacker might be able to modify or interact with internal resources in a limited way.
- No Availability Impact: This vulnerability does not directly affect the availability of the Ghost service.
- Risk to Cloud Environments: The ability to access the `169.254.169.254` metadata endpoint is particularly critical in cloud environments, as it can lead to the compromise of cloud credentials and further lateral movement.
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Sources:
Reported By: github.com
Extra Source Hub:
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