CVE-2026-52766: YesWiki vulnerable to unauthenticated arbitrary page deletion via `{{erasespamedcomments}}` action

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.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 47: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 47% of all scored CVEs (low). 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 yeswiki/yeswiki (Composer (PHP)) < 4.6.6, fixed in 4.6.6. Check your lockfile, including transitive dependencies.

What it is

YesWiki is a wiki system written in PHP. Prior to version 4.6.6, the {{erasespamedcomments}} wiki action (actions/EraseSpamedCommentsAction.php) accepts a suppr[] array from POST and deletes every wiki page whose tag appears in that array, with no authorization check anywhere in the action body or in the page-deletion path it invokes. Combined with YesWiki's allow-by-default action ACL model, any user who has page write access, which is the default for everyone (defaultwriteacl='') on a fresh install can permanently delete arbitrary wiki pages, including the front page, admin pages, and pages owned by other users. This issue has been patched in version 4.6.6.

From the GitHub advisory

Summary

The {{erasespamedcomments}} wiki action (actions/EraseSpamedCommentsAction.php) accepts a suppr[] array from POST and deletes every wiki page whose tag appears in that array, with no authorization check anywhere in the action body or in the page-deletion path it invokes. Combined with YesWiki's allow-by-default action ACL model, any user who has page write access, which is the default for everyone (defaultwriteacl='') on a fresh install can permanently delete arbitrary wiki pages, including the front page, admin pages, and pages owned by other users.

The action's delete() callee is PageManager::deleteOrphaned(), which despite its name does not check whether the target page is orphaned: it issues an unconditional DELETE against pages, links, acls, triples, referrers, and tags tables.

Details

Three issues compose the vulnerability.

Weakness type: CWE-276, CWE-862.

Product: yeswiki/yeswiki (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-09-04

Affected and fixed versions

Severity scores

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

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 poc, automatable yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.58% probability of exploitation activity in the next 30 days; percentile 47.

Timeline

• 2026-07-09 — GitHub-reviewed advisory GHSA-6x7x-gcmf-7r8x published (critical)
• 2026-09-04 — CVE record published by GitHub_M
• 2026-09-09 — CVE record last updated

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-6x7x-gcmf-7r8x github.com
2. CVE.org record CVE-2026-52766 cve.org
3. NVD entry CVE-2026-52766 nvd.nist.gov

Other references from the CVE record and advisory

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

Critical Composer (PHP) advisories · Today’s Security Digest