CVE-2026-122127 in ipfixcol2
Summary
by MITRE • 11/04/2026
CESNET ipfixcol2 2.7.1 before 2.9.0 contains a heap-based buffer overflow in Lz4Decoder.cpp that allows unauthenticated network peers to write past heap buffers. Attackers can declare a small ring buffer_size followed by a large decompressed_size to write up to 65535 controlled bytes and crash the collector.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in CESNET ipfixcol2 versions prior to 2.9.0 represents a critical security flaw rooted in improper input validation within the Lz4Decoder.cpp module. This heap-based buffer overflow occurs during the decompression process of data streams, specifically when handling inputs from unauthenticated network peers. The core technical issue stems from a logic error where the application fails to adequately verify that the size of the compressed data does not exceed the allocated memory capacity for the decompressed output. By manipulating specific parameters in the input stream, an attacker can exploit this discrepancy to force the system to write data beyond the boundaries of the intended heap buffer. This type of flaw is classically categorized under CWE-122, which denotes a heap-based buffer overflow, and often falls within the scope of CWE-400 regarding uncontrolled resource consumption if it leads to denial-of-service conditions through memory corruption or exhaustion.
The operational mechanism of this exploit relies on a specific sequence of crafted inputs designed to bypass standard size checks. An attacker initiates communication with the ipfixcol2 collector and declares a minimal ring buffer_size, which sets an expectation for limited data handling capacity. Subsequently, the attacker provides a significantly larger decompressed_size value in the stream metadata. When the Lz4Decoder processes this input, it attempts to allocate memory or write output based on the inflated decompressed size rather than validating against actual available heap space or logical constraints derived from the compressed payload. This mismatch allows up to 65535 bytes of attacker-controlled data to be written past the end of the allocated buffer. Such out-of-bounds writes can corrupt adjacent heap metadata, overwrite function return addresses on the stack if reachable via memory layout manipulation, or simply cause immediate application instability due to invalid memory access violations.
The impact of this vulnerability is primarily a denial of service against the IPFIX collector infrastructure. Since ipfixcol2 serves as a critical component in network traffic monitoring and security information management systems, its compromise disrupts the collection and processing of flow data essential for visibility into network activities. The immediate consequence described is the crash of the collector process, which halts all ongoing data ingestion from connected exporters. In more severe scenarios involving sophisticated exploitation techniques beyond simple crashing, such as heap spraying or precise memory corruption, this vulnerability could potentially be leveraged to achieve arbitrary code execution with the privileges of the ipfixcol2 service account. This aligns with ATT&CK technique T1498, Network Denial of Service, and potentially T1055, Process Injection, if the overflow is utilized for further lateral movement or persistence within the monitored environment.
Mitigation strategies must focus on immediate patching and defensive configuration adjustments. The primary remediation step is to upgrade ipfixcol2 to version 2.9.0 or later, where this heap-based buffer overflow has been addressed through improved input validation and bounds checking in the Lz4Decoder module. Until patches are applied, organizations should restrict network access to the IPFIX collector ports using firewall rules, ensuring that only trusted exporters can send data to the service. Additionally, implementing deep packet inspection or intrusion prevention systems capable of detecting anomalous stream sizes or malformed compression headers may help mitigate exploitation attempts by blocking suspicious traffic before it reaches the vulnerable application layer. Regular security audits and code reviews focusing on memory management functions are also recommended to prevent similar vulnerabilities in future software updates.