Executive Summary

CVE-2026-1813 is a vulnerability in bolo-blog bolo-solo versions up to 2.6.4, specifically in the FreeMarker Template Handler component within the file PicUploadProcessor.java. The issue arises from insufficient validation of the file argument during uploads, allowing attackers to perform unrestricted file uploads.

This flaw enables attackers to upload arbitrary files, including malicious FreeMarker template files (.ftl), which the application processes automatically. By overwriting these template files with malicious code, attackers can execute arbitrary commands on the server remotely.

The vulnerability can be exploited remotely without user interaction, and a public proof-of-concept exploit is available.

Useful 0 Not Useful 0

Impact Analysis

This vulnerability can lead to remote code execution (RCE) on the affected server, allowing attackers to run arbitrary system commands.

By exploiting the unrestricted file upload, attackers can overwrite FreeMarker template files with malicious code, which is then executed when the web pages are accessed.

The impact includes compromise of confidentiality, integrity, and availability of the system, potentially leading to full control over the server hosting bolo-solo.

Useful 0 Not Useful 0

Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring for suspicious POST requests to the /pic/upload endpoint, especially those containing multipart/form-data payloads attempting to upload files with unusual or malicious names such as FreeMarker template files (.ftl).'}, {'type': 'paragraph', 'content': 'A practical detection method is to inspect web server logs or use network monitoring tools to identify attempts to upload files to /pic/upload.'}, {'type': 'paragraph', 'content': 'Example commands to detect such activity include:'}, {'type': 'list_item', 'content': "Using grep to find POST requests to /pic/upload in web server logs: grep 'POST /pic/upload' /var/log/nginx/access.log"}, {'type': 'list_item', 'content': "Using tcpdump to capture HTTP POST traffic to /pic/upload: tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/pic/upload'"}, {'type': 'list_item', 'content': "Searching for uploaded .ftl files or suspicious file writes on the server filesystem, for example: find /path/to/bolo-solo -name '*.ftl' -mtime -7"}, {'type': 'paragraph', 'content': 'Additionally, monitoring for unexpected changes in FreeMarker template files or unusual file creation timestamps can help detect exploitation attempts.'}] [2, 3]

Useful 0 Not Useful 0

Mitigation Strategies

Currently, no official patches or countermeasures have been provided by the bolo-blog project for this vulnerability.

Immediate mitigation steps include:

• Restrict or disable the /pic/upload endpoint to prevent file uploads until a fix is available.
• Implement network-level controls such as firewall rules or web application firewall (WAF) rules to block or monitor suspicious upload attempts.
• Manually audit and monitor FreeMarker template files (.ftl) for unauthorized modifications.
• Consider replacing or upgrading the affected component or product if possible.

Because the vulnerability allows remote code execution via arbitrary file upload and template modification, immediate containment and monitoring are critical.

Useful 0 Not Useful 0

Compliance Impact

The vulnerability allows unrestricted file upload leading to remote code execution, which impacts the confidentiality, integrity, and availability of the system.

Such a compromise can result in unauthorized access to sensitive data or disruption of services, potentially violating data protection regulations like GDPR and HIPAA that require safeguarding personal and health information.

Because the vulnerability enables attackers to execute arbitrary code remotely, it increases the risk of data breaches and unauthorized data manipulation, which are critical compliance concerns under these standards.

No known mitigations or responses have been provided by the project, which may further exacerbate compliance risks if the vulnerability is exploited.

Useful 0 Not Useful 0