UN officials have cited both Israel and the Lebanese army for reports of smuggling.
Their mission was to probe Lebanon's monitoring system along its 320km border with Syria and not to uncover cases of arms smuggling.
Syria denied involvement in any illegal transfers and was not included in the assessment.
The report, submitted to security council members, said: "The present state of border security was insufficient to prevent smuggling, in particular the smuggling of arms, to any significant extent".
"Not a single on-border or near-border seizure of smuggled arms has been documented to the team," read the report.
Weaknesses were attributed to poor border layout and control points and a lack of fixed procedures.
The report suggests that Lebanon establish a multi-agency mobile force focusing on arms smuggling and have an intelligence unit that could combine information from different agencies.
International security experts should bolster the force, while a dedicated border guard agency should eventually be created, the report said.
Other recommendations include moving the official crossing points closer to the actual border.
The security council and Ban Ki-moon, the UN secretary-general, have strongly backed Lebanon's government despite its standoff with Hezbollah.
Last month, the council approved a special tribunal to try the suspected killers of Rafiq al-Hariri, the former Lebanese prime minister.
The report by experts from Denmark, Algeria, Germany, Jamaica and Switzerland largely avoided addressing the issue of Lebanese-Syrian relations - suggesting that Lebanese border officials co-operate with their Syrian counterparts.