In a report from the Huawei Cyber Security Evaluation Centre (HCSEC) Oversight Board - which was set up by the UK's National Cyber Security Centre - it is said while there is no direct evidence of state-backed espionage, the company's "basic engineering competence and cyber security hygiene" has been criticised.
The report says: "HCSEC has continued to find serious vulnerabilities in the Huawei products examined.
"Several hundred vulnerabilities and issues were reported to UK operators to inform their risk management and remediation in 2018.
"Some vulnerabilities identified in previous versions of products continue to exist."
It is also noted that a potential attacker with "knowledge of these vulnerabilities and sufficient access to exploit them" could impact the network's operation, or even "access user traffic or reconfiguration of the network elements".
That said, the report also clarifies that "exploitation of vulnerabilities" is made harder due to the security management of UK operators.
According to the Financial Times - which detailed the new report - a final decision on using Huawei's equipment in 5G networks is to be made over the coming weeks.
The report adds: "The Oversight Board continues to be able to provide only limited assurance that the long-term security risks can be managed in the Huawei equipment currently deployed in the UK."