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How CVE-2026-53949 Works
Ghost is a Node.js-based content management system that exposes public API endpoints for fetching content. These endpoints accept a `filter` query parameter, allowing clients to refine queries—for example, `filter=slug:example` to retrieve a specific post.
The vulnerability stems from incomplete validation of these filters. While Ghost’s API is designed to restrict which fields can be queried publicly, the validation logic could be partially bypassed. An attacker could craft a series of `filter` requests containing private field names (e.g., password, email) and send them iteratively to the Content API. If a field exists and is queryable, the API would return it, effectively allowing a brute-force enumeration of private fields.
The severity of the exposure depends on the underlying database:
– SQLite: Password hashes are stored in plain text within the database. Successful exploitation grants the attacker full access to these hashes.
– MySQL: Password hashes are stored with case sensitivity. The bypass reveals the hashes but loses case information, rendering the stolen hashes largely useless for further brute-force attacks.
The vulnerability affects all self-hosted Ghost instances from version 5.46.1 up to and including 6.21.1. Ghost(Pro) hosted instances were patched automatically and are not affected. The fix was released in version 6.21.2, which strengthens filter validation to prevent private fields from being exposed via the public API.
DailyCVE Form:
Platform: ……. Ghost CMS
Version: …….. 5.46.1–6.21.1
Vulnerability :…… Filter validation bypass
Severity: ……. 5.3 (Medium)
date: ………. 2026-06-24
Prediction: ……. 2026-06-24 (already released)
What Undercode Say: Analytics
The vulnerability resides in the filter parsing logic of Ghost’s Content API. Below is a conceptual breakdown of the attack surface and validation flaw.
Affected endpoint pattern:
GET /ghost/api/content/{resource}/?filter={crafted_filter}
Vulnerable filter examples (conceptual):
GET /ghost/api/content/posts/?filter=users.password:12345 GET /ghost/api/content/posts/?filter=authors.email:[email protected] GET /ghost/api/content/posts/?filter=users.password:
Bypass technique (conceptual):
The attacker enumerates private field names by injecting them into the `filter` parameter. If the field exists and is not properly blocked, the API returns data containing that field.
Workaround regex pattern (case-insensitive):
filter=[^&](password|email)
This pattern can be used in a WAF or reverse proxy to block malicious requests.
CVSS Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
This yields a base score of 5.3 (Medium), indicating low confidentiality impact with no impact on integrity or availability.
How Exploit
Exploitation requires no authentication and can be performed remotely over the network. The attacker sends a series of GET requests to the Content API with progressively crafted `filter` parameters.
Example attack flow:
- Identify a vulnerable Ghost instance (version between 5.46.1 and 6.21.1).
- Send a request to enumerate a private field:
GET /ghost/api/content/posts/?filter=users.password:
- If the field is exposed, the response will include password hash data.
- Iterate over other private fields (e.g.,
users.email,authors.password,authors.email). - For SQLite backends, extract full password hashes and proceed with offline cracking.
Note: The attack is a brute-force enumeration, meaning each request tests one field or value. While time-consuming, it is feasible given the low complexity and lack of rate limiting on many deployments.
Protection from this CVE
Immediate (Recommended):
- Upgrade Ghost to v6.21.2 or later.
- Docker: Pull the latest official image and restart the container.
- Ghost-CLI: Run `ghost update` to apply the patch.
Temporary Mitigation (if upgrade is not possible):
- Deploy a WAF or reverse proxy rule to block requests containing suspicious filter patterns.
- Example NGINX rule:
location /ghost/api/content/ { if ($args ~ "filter=[^&](password|email)") { return 403; } proxy_pass http://ghost_backend; } - Alternatively, use the following Apache `.htaccess` rule:
RewriteCond %{QUERY_STRING} filter=[^&](password|email) [bash] RewriteRule ^ghost/api/content/ - [bash]
Long-term:
- Regularly audit and update Ghost to the latest stable version.
- Consider using a hosted Ghost(Pro) instance where patches are applied automatically.
- Monitor API access logs for unusual filter patterns.
Impact
Confidentiality Exposure:
- Private fields such as `password` and `email` can be enumerated via brute force.
- If SQLite is used, password hashes are fully exposed, enabling offline cracking attacks.
- If MySQL is used, password hash case information is lost, reducing the risk but still exposing sensitive metadata.
Affected Versions:
- Ghost v5.46.1 through v6.21.1 (inclusive).
Patch Status:
- Fixed in v6.21.2.
CVSS Score:
- 5.3 (Medium) – Network exploitable, low attack complexity, no privileges required, low confidentiality impact.
References:
- GitHub Security Advisory: GHSA-jx35-x7fj-vgpr
- CVE Record: CVE-2026-53949
- Debian Security Tracker: CVE-2026-53949
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Sources:
Reported By: github.com
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