Executive Summary

CVE-2026-26477 is a vulnerability in DokuWiki version 2025-05-14b that allows a remote attacker to cause a denial of service (DoS). The issue exists in the media upload functionality, specifically in the media_upload_xhr() function within the inc/media.php file.

The vulnerability arises because the qqfile parameter, which identifies the uploaded file, is used directly without validating the directory depth. Filenames containing colon characters (:) are interpreted as directory separators, so a filename like '123:123.pdf' is treated as a nested path '123/123.pdf'.

An attacker can exploit this by crafting a filename with a large number of colons (for example, qqfile=123:123:...:123.pdf with 1000+ colons), causing the system to recursively create thousands of nested directories. This leads to excessive CPU usage due to intensive filesystem operations, ultimately exhausting server resources and causing a denial of service.

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Impact Analysis

This vulnerability can impact you by causing a denial of service on the affected DokuWiki server. An attacker can exploit it to exhaust server CPU resources by forcing the creation of thousands of nested directories through a specially crafted filename.

As a result, legitimate requests to the server will be blocked or delayed, disrupting normal service availability.

There is no risk of data exfiltration or other types of compromise associated with this vulnerability; the impact is limited to service disruption.

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Detection Guidance

This vulnerability can be detected by monitoring for unusual POST requests to the endpoint /lib/exe/ajax.php that include the qqfile parameter with filenames containing multiple colon characters (:). Such requests may indicate attempts to exploit the directory traversal and resource exhaustion flaw.

A practical detection method is to inspect web server logs or use network monitoring tools to identify requests where qqfile contains many colon-separated segments, for example qqfile=test1:test2:test3.pdf or with hundreds of colons.

You can use commands like the following to search your web server logs for suspicious qqfile parameters:

• grep -E 'qqfile=.*(:.*){10,}' /path/to/access.log
• awk '/qqfile=/ && gsub(":",":") > 10' /path/to/access.log

Additionally, testing with tools like Burp Suite by sending POST requests with qqfile parameters containing many colon characters can confirm if the system is vulnerable.

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Mitigation Strategies

Immediate mitigation steps include restricting or filtering incoming requests to prevent qqfile parameters with excessive colon characters from reaching the application.

You can implement web application firewall (WAF) rules to block requests where qqfile contains multiple colons, or limit the length and character set of the qqfile parameter.

Another step is to monitor server resource usage and block IP addresses generating suspicious requests that cause high CPU or filesystem activity.

Ultimately, updating or patching the Dokuwiki installation to a version where this vulnerability is fixed is recommended once available.

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Compliance Impact

The vulnerability causes a denial of service by exhausting server resources through excessive filesystem operations. It does not involve data exfiltration or compromise of confidentiality or integrity.

Since there is no risk of data breach or unauthorized access to personal or sensitive information, the impact on compliance with standards like GDPR or HIPAA is minimal or indirect, primarily related to availability.

However, denial of service could affect availability requirements under these regulations, potentially impacting service continuity obligations.

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