Bug 2481520 (CVE-2026-48691)

Summary: CVE-2026-48691 fastnetmon: integer overflow in the BGP AS_PATH attribute encoder
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: urgent    
Version: unspecifiedKeywords: Security
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OS: Linux   
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Bug Depends On: 2482717, 2482718    
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Description OSIDB Bzimport 2026-05-26 17:01:51 UTC 
FastNetMon Community Edition through 1.2.9 contains an integer overflow in the BGP AS_PATH attribute encoder. In src/bgp_protocol.hpp, the IPv4UnicastAnnounce::get_attributes() function computes attribute_length as 'sizeof(bgp_as_path_segment_element_t) + this->as_path_asns.size() * sizeof(uint32_t)' and stores it in a uint8_t field (line 600-605). Since uint8_t can only hold values 0-255, an AS_PATH containing more than 63 ASNs (2 + 64*4 = 258 > 255) causes silent truncation. The truncated length is used for buffer sizing, while the actual data written is the full untruncated amount, resulting in a heap buffer overflow. Similarly, the path_segment_length field at line 621 is also uint8_t, truncating with more than 255 ASNs.