YesWiki Vulnerable to Reflected XSS via Unescaped Archived-Revision `time` Parameter in `handlers/page/show.php`

In practice, the payload must begin with a real archived revision timestamp. A completely invalid time value does not reach the archived branch because YesWiki only updates the current page object when the revision lookup returns a non-empty row.

During local validation on the official doryphore 4.6.5 package, the exploit worked because MySQL accepted a malformed timestamp string as matching an existing archived revision row. For example, the following expression was coerced to the stored revision time:

CAST(CONCAT('2026-05-24 04:30:00', CHAR(34), CHAR(62), CHAR(60), 'script', CHAR(62), 'alert(1)', CHAR(60), '/script', CHAR(62)) AS DATETIME)

and the corresponding query predicate still matched the archived row:

WHERE time = '2026-05-24 04:30:00"><script>alert(1)</script>'

This means a payload can begin with a valid archived revision timestamp, still resolve to the archived revision, and then be reflected unescaped into the hidden HTML field.

For comparison, tools/bazar/handlers/page/show__.php around lines 13-14 escapes the same time value with htmlspecialchars(), which shows that the core handler's behavior is inconsistent and unsafe.

This issue maps to CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').

PoC

1. Set up a vulnerable YesWiki instance. This was validated locally on the official doryphore 4.6.5 release.
2. Use a target page that has at least one archived revision. Any page with revision history is sufficient.
3. Confirm the victim has the rights needed to reach the vulnerable sink:
   • The victim must have read access to the page.
   • The victim must have write access to the page.
   • On the default validation install, these rights were available anonymously on public pages such as PagePrincipale, so no login was required in that configuration.
4. Identify the timestamp of an archived revision. In the validated setup, an archived PagePrincipale revision existed at 2026-05-24 04:30:00.
5. Send the victim a crafted URL that starts with that valid archived revision timestamp and then appends an attribute-breaking payload:

http://127.0.0.1:8085/PagePrincipale?time=2026-05-24%2004:30:00%22%3E%3Cscript%3Ealert(1)%3C/script%3E%3Cinput%20value=%22

6. Open the URL in a browser as a victim who has the required read and write rights.
7. Observe that YesWiki still loads the archived revision view and displays the archived-revision warning block, proving the malformed time value matched the stored archived revision.
8. Inspect the returned HTML. The response contains the injected payload inside the hidden form field:

<input type="hidden" name="time" value="2026-05-24 04:30:00"><script>alert(1)</script><input value="" />

9. The browser executes the injected JavaScript in the YesWiki origin. A simple payload such as alert(1) demonstrates code execution; a real payload could read browser-accessible data or perform actions in the victim's session.

Impact

This is a reflected XSS vulnerability in the archived-revision workflow.

The practical access model is:

• The attacker only needs to send a crafted link.
• The victim must have read and write access to the target page.
• The target page must have at least one archived revision.
• On deployments where anonymous visitors can edit public pages, the issue can be exploited against unauthenticated visitors as well.

An attacker may be able to:

• Execute arbitrary JavaScript in the victim's browser.
• Steal browser-accessible sensitive data.
• Perform actions as the victim inside YesWiki.
• Abuse the trusted YesWiki origin for phishing, UI redressing, or follow-on attacks.