CVE-2026-1813 is a vulnerability identified in the bolo-blog project's bolo-solo software, specifically affecting versions 2.6.0 through 2.6.4. The issue resides in the src/main/java/org/b3log/solo/bolo/pic/PicUploadProcessor.java file, within the FreeMarker Template Handler component. The vulnerability stems from insufficient validation of the File argument, which leads to an unrestricted file upload capability. This flaw allows remote attackers to upload arbitrary files to the server without requiring authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The vulnerability has a CVSS 4.0 base score of 5.3, categorizing it as medium severity. The exploit has been publicly disclosed, increasing the risk of exploitation, although no active exploits have been reported in the wild yet. The bolo-solo project was notified early but has not yet responded or issued a patch. Successful exploitation could allow attackers to upload malicious scripts or executables, potentially leading to remote code execution, website defacement, data theft, or server compromise. The vulnerability's impact is heightened by the fact that it requires low privileges (PR:L) but no user interaction, making it easier to exploit in automated attacks. The lack of a patch and public exploit availability necessitate immediate defensive measures by users of the affected software.

For European organizations using bolo-solo, this vulnerability poses a significant risk to web server integrity and data confidentiality. Attackers could leverage the unrestricted upload to deploy web shells or malware, leading to unauthorized access, data breaches, or service disruption. Organizations operating public-facing websites or blogs with bolo-solo are particularly vulnerable to defacement or reputational damage. The medium severity rating reflects moderate impact potential; however, the ease of remote exploitation without user interaction increases the likelihood of attacks. In sectors such as media, education, or government where bolo-solo might be deployed, the impact could extend to sensitive information exposure or operational disruption. Additionally, the absence of an official patch increases the window of exposure, necessitating proactive mitigation. The threat could also facilitate lateral movement within networks if attackers gain footholds via compromised web servers.

Given the absence of an official patch, European organizations should implement immediate compensating controls. These include restricting file upload permissions to trusted users only and disabling uploads if not essential. Implement strict server-side validation to allow only specific file types and sizes, rejecting any suspicious or executable files. Employ web application firewalls (WAFs) to detect and block malicious upload attempts based on known exploit patterns. Monitor server logs for unusual upload activity or access patterns indicative of exploitation attempts. Isolate the web server environment to limit potential damage from a compromised instance. Regularly back up website content and configurations to enable rapid restoration if defacement or compromise occurs. Engage with the bolo-solo community or maintainers to track patch releases and apply updates promptly once available. Conduct security awareness training for administrators managing bolo-solo deployments to recognize and respond to suspicious activities.