CVE-2026-61548: rsyslog Stack-based Buffer Overflow

Vulnerability summary

CVE-2026-61548 is a high (CVSS 8.1) Stack-based Buffer Overflow vulnerability in rsyslog. EPSS estimates a 0.94% chance of exploitation in the next 30 days, higher than 60.2% of scored vulnerabilities.

Timeline

1. 18-09-2026
   PublishedVulnerability first disclosed.
2. 21-09-2026
   Last modifiedVulnerability information updated.

Description

Rsyslog is a rocket-fast system for log processing. From 7.5.4 until 8.2606.0, the optional mmpstrucdata plugin's parseSD_PARAM function in plugins/mmpstrucdata/mmpstrucdata.c stores RFC5424 parameter values in a fixed pVal[32 * 1024] stack buffer and calls parsePARAM_VALUE without supplying the destination size. A remote unauthenticated attacker whose crafted RFC5424 message reaches an action using mmpstrucdata can provide a structured-data parameter larger than that buffer when MaxMessageSize permits it, causing an attacker-controlled stack overwrite. Deployments that do not install and use the plugin, or whose effective message-size limit remains below the required threshold, are not affected by this issue. The demonstrated impact is a crash and interruption of log collection; code execution is not demonstrated. This issue is fixed in version 8.2606.0.

• CWE-121Stack-based Buffer OverflowA stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).