CVE-2026-41876: R-SOFT DMS RCE Vulnerability

CVE-2026-41876 Overview

CVE-2026-41876 is an OS Command Injection vulnerability [CWE-78] in the R-SOFT Document Management System (DMS). The flaw resides in the konwertujAction() function, which is responsible for document conversion. The function passes unsanitized file paths and format parameters into shell command execution. An authenticated attacker can inject arbitrary shell commands and execute them with the privileges of the web server user. The issue is fixed in versions v3.19-2752 and v3.17-2580.

Critical Impact
Authenticated attackers can achieve arbitrary command execution on the underlying server, leading to full compromise of confidentiality, integrity, and availability of the DMS host.

Affected Products

R-SOFT DMS versions prior to v3.19-2752
R-SOFT DMS versions prior to v3.17-2580
Deployments exposing the document converter endpoint to authenticated users

Discovery Timeline

2026-07-10 - CVE-2026-41876 published to the National Vulnerability Database (NVD)
2026-07-10 - Last updated in NVD database

Technical Details for CVE-2026-41876

Vulnerability Analysis

The vulnerability affects the konwertujAction() function inside R-SOFT DMS. This function orchestrates document format conversion by invoking external shell utilities. The function accepts user-controlled input for file paths and target format parameters. These parameters are concatenated into a shell command string without proper sanitization or argument escaping.

An authenticated attacker can craft input containing shell metacharacters such as ;, |, &&, or backticks. When konwertujAction() builds and executes the command, the injected payload runs alongside the intended converter. Commands run under the identity of the web server process. This provides a foothold for lateral movement, data exfiltration, and persistent access. Additional technical detail is available in the CERT Polska advisory for CVE-2026-41876.

Root Cause

The root cause is missing input validation and unsafe construction of operating system commands. The function relies on string concatenation to build shell invocations rather than using parameterized process execution APIs. File path and format inputs are trusted without allowlisting or metacharacter filtering.

Attack Vector

Exploitation requires network access to the DMS web interface and valid authenticated credentials with permission to trigger document conversion. The attacker submits a conversion request where the file path or format parameter contains an appended shell command. The web application invokes the converter, and the injected command executes on the host. No user interaction is required beyond the attacker's own authenticated session.

Detection Methods for CVE-2026-41876

Indicators of Compromise

Unexpected child processes spawned by the R-SOFT DMS web server process, such as /bin/sh, bash, cmd.exe, or system utilities like curl, wget, nc, or powershell.
HTTP request logs to the document conversion endpoint containing shell metacharacters (;, |, `, $(, &&) in file path or format parameters.
Outbound network connections from the DMS host to unfamiliar external IP addresses shortly after conversion requests.
New or modified files in web-accessible directories, indicating webshell deployment.

Detection Strategies

Monitor process ancestry for shell interpreters or reconnaissance binaries whose parent process is the DMS web server or its PHP/Java runtime.
Inspect web server access logs for requests to the konwertujAction route containing URL-encoded shell operators.
Correlate authenticated DMS sessions with unusual outbound traffic or file writes on the host.

Monitoring Recommendations

Enable command-line auditing on the DMS host and forward logs to a centralized SIEM for retention and search.
Alert on any process launched by the DMS service account that is not part of the documented converter binary set.
Track authentication events for DMS accounts with conversion privileges and flag anomalous session sources.

How to Mitigate CVE-2026-41876

Immediate Actions Required

Upgrade R-SOFT DMS to version v3.19-2752 or v3.17-2580 without delay.
Restrict access to the DMS application to trusted networks using VPN or IP allowlisting until the patch is applied.
Rotate credentials for any DMS accounts that had conversion privileges during the exposure window.
Review web server logs for prior exploitation attempts targeting the konwertujAction endpoint.

Patch Information

The vendor addressed CVE-2026-41876 in R-SOFT DMS v3.19-2752 and v3.17-2580. Administrators should apply the appropriate patched release for their branch. Refer to the CERT Polska advisory for release details and vendor coordination information.

Workarounds

Remove or disable the document conversion feature until upgrade is possible.
Revoke conversion privileges from non-administrative user roles to reduce the pool of authenticated attackers.
Run the DMS web server process under a least-privilege account with no shell access and restricted filesystem permissions.
Deploy a Web Application Firewall (WAF) rule to block requests containing shell metacharacters in conversion parameters.

bash

# Example WAF rule pattern to block shell metacharacters in conversion requests
# (ModSecurity-style pseudo rule - adapt to your WAF syntax)
SecRule REQUEST_URI "@contains konwertujAction" \
  "chain,deny,status:403,id:1041876,msg:'Possible CVE-2026-41876 command injection'"
  SecRule ARGS "@rx [;|&`$()<>]" "t:urlDecodeUni"