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CVE-2026-52767 – Unauthenticated Signature-Verification Bypass (ActivityPub) – YesWiki 4.6.2–4.6.5

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Summary

CVE-2026-52767 is a cryptographic signature verification bypass (CWE-347) in YesWiki’s ActivityPub implementation, affecting versions 4.6.2 through 4.6.5. The flaw lets a remote, unauthenticated attacker submit forged ActivityPub payloads that YesWiki treats as validly signed. The issue is rated High severity (CVSS 8.2).

Technical details

  • Root cause: HttpSignatureService::verifySignature() (in tools/bazar/services/HttpSignatureService.php) checks the result of PHP’s openssl_verify() using a loose negation, if (!openssl_verify(...)).
  • openssl_verify() can return 1 (valid), 0 (invalid), or -1 (internal error). PHP evaluates -1 as truthy, so !(-1) is false — an internal verification error is silently treated as a successful signature check.
  • Two conditions can trigger the -1 return: (1) a DSA or EC public key presented against an RSA-only algorithm specification, and (2) on older PHP/OpenSSL combinations, use of an unrecognized digest name.
  • Attack vector is network-based, requires no authentication and no user interaction; an attacker crafts an ActivityPub request that fails proper signature verification but is nonetheless accepted and processed.
  • Impact: unauthenticated create/update/delete of Bazar entries, content injection and site defacement, pollution of the underlying triple-store, and SEO poisoning via injected HTML content.

Affected software

  • YesWiki v4.6.2
  • YesWiki v4.6.3
  • YesWiki v4.6.4
  • YesWiki v4.6.5

Severity

  • CVSS v3.1 Base Score: 8.2 (High)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L

Mitigation and recommended actions

  • Immediate: upgrade to YesWiki v4.6.6 or later, which fixes the signature verification logic.
  • If patching is not immediately possible: restrict or disable exposure of the ActivityPub/Bazar endpoints at the network or reverse-proxy layer until the upgrade can be applied, and monitor for unexpected Bazar entry creation/modification/deletion activity.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Named response header (link): YesWiki-
  • Raw response body: yeswiki.net

References

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How IONIX’s External Exposure Management Platform Detects and Validates
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1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

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By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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