high · 8.3CVE-2026-52769Jul 9, 2026

CVE-2026-52769: YesWiki Unauthenticated SSRF via ActivityPub Signature keyId

Pranav Khune
Penetration Testing Team Lead, SecureLayer7

An unauthenticated attacker can trick YesWiki into making arbitrary outbound HTTP requests to any host, including internal cloud metadata endpoints, by setting the keyId field in an HTTP Signature…

Packageyeswiki/yeswiki
Ecosystemcomposer
Affected>= 4.6.2, < 4.6.6
Fixed in4.6.6

The problem

The public ActivityPub inbox route (POST /?api/forms/{formId}/actor/inbox) accepts an HTTP Signature header and immediately fetches the URL in keyId before doing any cryptographic check or URL validation. No session, token, or prior knowledge is required.

The only precondition is that ActivityPub be enabled on at least one Bazar form (bn_activitypub_enable = '1'). Affected versions are 4.6.2 through 4.6.5 of yeswiki/yeswiki.

Proof of concept

A working proof-of-concept for CVE-2026-52769 in yeswiki/yeswiki, with the exact payload below.

http
POST /?api/forms/1/actor/inbox HTTP/1.1
Host: target.example
Content-Type: application/activity+json
Signature: keyId="http://169.254.169.254/latest/meta-data/iam/security-credentials/ec2-role",algorithm="rsa-sha256",headers="x",signature="y"

{}

In HttpSignatureService::verifySignature(), the Signature header is parsed with parse_ini_string() and the keyId value is passed directly to httpClient->request('GET', $sigConf['keyId']) at line 96. There is no scheme check, no IP allowlist, and no private-range filter.

The patch (commit 87e627f) adds URL validation before the outbound fetch, blocking private IP ranges, link-local addresses (including 169.254.169.254), and non-HTTPS schemes. The root cause is CWE-918: the attacker-controlled keyId string is used as a fetch target with no sanitization, making the server an open proxy for the attacker.

A 500 response containing "Missing public key" in the exception message confirms the fetch completed, giving the attacker a timing and error oracle for port scanning and internal service enumeration.

The fix

Upgrade to yeswiki/yeswiki 4.6.6, which validates the keyId URL and blocks requests to private or link-local addresses before any outbound HTTP call is made. If an immediate upgrade is not possible, disable ActivityPub on all Bazar forms (bn_activitypub_enable = '0') to close the exposed route.

Reporter not attributed.

References: [1][2][3]

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