VulnerabilityPublished 9 Jul 2026

CVE-2026-52767: yeswiki/yeswiki · YesWiki Vulnerable to Unauthenticated ActivityPub Signature-Verification Bypass via `!openssl_verify(...)` accepting `int(-1)`

Affects yeswiki/yeswikiSource GCVE Database

Compare

Not known to be exploited · CVSS 8.2 High : upgrade to 4.6.6 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

8.2High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 28% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.6.6

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 9 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade yeswiki/yeswiki to 4.6.6.

Affected software

Product	Affected	Fixed in
Packagistyeswiki/yeswiki	Affected >=4.6.2 <4.6.6	Fixed in 4.6.6

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

If you cannot patch yet, users should consider mitigating by avoiding use of PHP 8.3 with OpenSSL 3.x in affected YesWiki versions or by implementing stricter signature verification logic that correctly handles the -1 return value from openssl_verify(). Specifically, the code should explicitly check for the -1 return and treat it as a verification failure. Monitor vendor channels for an official patch and apply it promptly once released.

Description

YesWiki versions 4.6.2 through 4.6.5 contain a vulnerability in the HttpSignatureService::verifySignature() method where the result of PHP's openssl_verify() is checked using a loose boolean negation. Because openssl_verify() can return -1 on certain errors (such as using a DSA public key with an RSA algorithm), which evaluates as truthy in PHP, the signature verification failure is bypassed. This allows unauthenticated attackers to send malicious ActivityPub requests that are processed as valid, enabling unauthorized Create, Update, or Delete operations.

Impact

The vulnerability allows unauthenticated attackers to bypass signature verification and submit malicious ActivityPub requests to YesWiki's actor inbox endpoint. This can lead to unauthorized creation, update, or deletion of entries within the application, compromising data integrity. There is no requirement for a valid session or CSRF token, making exploitation straightforward once the attacker controls an actor document with a crafted public key. The digest header is enforced but easily satisfied by the attacker. The impact is high due to the ability to perform unauthorized state changes without authentication.

Summary

The vulnerability arises from improper handling of the openssl_verify() return value in YesWiki's HttpSignatureService::verifySignature() method. The code uses if (!openssl_verify(...)) to detect signature verification failure. However, openssl_verify() can return four values: 1 (valid), 0 (invalid), -1 (internal error), and false (argument validation failure). The check incorrectly treats -1 as a successful verification due to PHP's truthiness rules, skipping the exception throw. An attacker can exploit this by providing a DSA public key with an RSA-SHA256 algorithm, causing openssl_verify() to return -1 and bypass signature verification. The attacker can then send unauthenticated POST requests to the actor inbox endpoint, which YesWiki processes, allowing unauthorized state mutations. This affects YesWiki versions >=4.6.2 and <4.6.6.

CWE-347Improper Verification of Cryptographic Signature (opens in a new tab)
Base weaknessOWASP Top 10 A04:2025: Cryptographic Failures (opens in a new tab)
The product does not verify, or incorrectly verifies, the cryptographic signature for data.
OWASP Cheat Sheets
XML Security (opens in a new tab)
REST Security (opens in a new tab)
JSON Web Token for Java (opens in a new tab)
REST Assessment (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.2 (opens in a new tab)
V3.5.3 (opens in a new tab)
V13.2.6 (opens in a new tab)
Attack patterns
Padding Oracle Crypto Attack (opens in a new tab)
Signature Spoofing by Improper Validation (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Jul 2026, 09:56 UTC

WeaknessesCWE-347

Technical details

References

Community reviews

Related threats