CVE-2026-19654 in rsyslog
Summary
by MITRE • 08/12/2026
A unauthenticated remote peer may lead rsyslogd to crash due to a flaw in the optional imptcp module. A crafted input sequence during oversize-frame recovery can cause an invalid internal message length and terminate rsyslogd. No confidentiality or integrity impact, privilege escalation, or code execution has been identified. imtcp and the default imptcp framing modes are not affected.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/12/2026
The vulnerability described represents a denial of service condition within the rsyslogd daemon that specifically affects the optional imptcp module when processing oversized frame recovery scenarios. This flaw exists in the handling of crafted input sequences during the recovery process of oversized network frames, which triggers an invalid internal message length calculation that ultimately causes the rsyslogd process to terminate unexpectedly. The issue is classified as a remote unauthenticated vulnerability since any external peer can potentially exploit this condition without requiring prior authentication or elevated privileges. The technical implementation involves the imptcp module's failure to properly validate or sanitize input data during oversize-frame recovery operations, leading to an internal state corruption that manifests as process termination.
The operational impact of this vulnerability extends beyond simple service disruption as it affects the reliability and availability of syslog processing capabilities on systems running rsyslogd. When exploited, the vulnerability can cause continuous service interruptions if not properly addressed, potentially compromising system monitoring and logging infrastructure that relies on rsyslog for centralized log collection and management. The affected module operates within a specific configuration context where oversized frames are processed through recovery mechanisms, making this issue particularly relevant in environments with high-volume network logging or systems that receive large syslog messages from various network devices. This vulnerability directly impacts the system's ability to maintain continuous logging operations, which could affect compliance requirements and incident response capabilities.
Security implications of this vulnerability align with CWE-122 which describes "Heap Overflow" conditions where improper handling of memory can lead to process termination or system instability. The flaw demonstrates characteristics consistent with buffer over-read or invalid memory access patterns that occur during frame recovery processing, though no evidence suggests code execution or privilege escalation capabilities exist within the scope of this vulnerability. The attack vector requires only network connectivity to the rsyslogd service and does not require authentication, making it particularly concerning for systems exposed to untrusted networks or internet-facing services. This vulnerability also relates to ATT&CK technique T1499 which covers Network Denial of Service attacks that target system availability through various mechanisms including process termination.
Mitigation strategies should focus on immediate configuration adjustments such as disabling the problematic imptcp module when not required, implementing proper network segmentation to limit access to syslog services, and applying updated rsyslogd versions that contain patches for this specific flaw. System administrators should also consider implementing monitoring solutions to detect unusual process termination patterns or service disruptions related to logging infrastructure. The fix typically involves validating input data during oversize-frame recovery operations and implementing proper bounds checking mechanisms within the imptcp module to prevent invalid internal state modifications. Additionally, organizations should review their network access controls to ensure that only trusted entities can connect to syslog services, reducing the attack surface for this particular vulnerability while maintaining operational logging capabilities through alternative means such as the unaffected imtcp module or other logging solutions.