CVE-2026-48691: Pavel-odintsov Fastnetmon buffer overflow (CVSS 9.8)

Description

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Pavel-odintsov Fastnetmon≤ 1.2.9

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

https://github.com/pavel-odintsov/fastnetmonProduct
https://github.com/pavel-odintsov/fastnetmon/blob/master/src/bgp_protocol.hppProduct
https://lorikeetsecurity.com/blog/fastnetmon-cve-2026-48691-bgp-as-path-overflowThird Party Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-48691 being actively exploited?

CVE-2026-48691 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.57%.

How severe is CVE-2026-48691?

CVE-2026-48691 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.57% probability of exploitation.

Which products are affected by CVE-2026-48691?

Affected products include Pavel-odintsov Fastnetmon.

How do I fix CVE-2026-48691?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

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