CVE-2026-28508: Idno Vulnerable to Unauthenticated SSRF via URL Unfurl Endpoint

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.7%, percentile 54: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 54% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes idno/known (Composer (PHP)) <= 1.6.3, fixed in 1.6.4. Check your lockfile, including transitive dependencies.

What it is

Idno is a social publishing platform. Prior to version 1.6.4, a logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content. This issue has been patched in version 1.6.4.

From the GitHub advisory

Summary A logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content.

Component: Idno/Pages/Service/Web/UrlUnfurl.php, Idno/Core/Session.php, Idno/Core/Actions.php Vulnerability Class: Server-Side Request Forgery (SSRF) Authentication Required: None CVSSv4 Base Score: 9.2 (High) - AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N Affected Endpoint: GET /service/web/unfurl?url= Handled by Idno\Pages\Service\Web\UrlUnfurl::getContent(). Affected Versions:

Code Flow Step 1 — Endpoint access control UrlUnfurl::getContent() (UrlUnfurl.php:36) enforces two access controls: $this->xhrGatekeeper(); $this->tokenGatekeeper();

Notably, the original authentication check ($this->gatekeeper()) was explicitly removed with the following comment left in the source:

This leaves the endpoint accessible to unauthenticated users, with only the two remaining gatekeepers as a barrier.

Weakness type: CWE-918.

Product: idno/known (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-03-06

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.75% probability of exploitation activity in the next 30 days; percentile 54.

Timeline

• 2026-03-02 — GitHub-reviewed advisory GHSA-fcrh-fqxh-6fx6 published (critical)
• 2026-03-06 — CVE record last updated
• 2026-03-06 — CVE record published by GitHub_M

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-fcrh-fqxh-6fx6 github.com
2. CVE.org record CVE-2026-28508 cve.org
3. NVD entry CVE-2026-28508 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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