Executive Summary

The vulnerability in Free5GC 4.2.0 arises because the system improperly accepts non-PrintableString values in fields where the specification requires PrintableString encoding. Specifically, in NGAP messages like NGSetupRequest, fields such as RANNodeName are supposed to contain only PrintableString characters, but Free5GC accepts arbitrary byte sequences instead.

This deviation from the ASN.1 specification can lead to type confusion, causing crashes or bugs when the malformed data is processed later. The vulnerability is due to a lack of strict ASN.1 type validation in Free5GC's NGAP message processing, which can be exploited remotely but with high complexity and difficult exploitability.

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Impact Analysis

This vulnerability can impact system stability and security by allowing malformed or maliciously crafted NGAP messages to be accepted and processed. This can lead to crashes or unexpected behavior in the Free5GC system, potentially disrupting network operations.

Since the vulnerability involves type confusion due to improper validation, attackers might exploit it to cause denial of service or other unintended effects, although the attack complexity is high and exploitability is difficult.

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Detection Guidance

This vulnerability can be detected by monitoring NGAP messages, specifically looking for NGSetupRequest messages containing RANNodeName Information Elements (IE) with non-PrintableString byte sequences that violate the ASN.1 PrintableString encoding rules.

Detection involves capturing and analyzing NGAP traffic to identify malformed RANNodeName fields that include invalid characters such as non-printable bytes (e.g., \x01\x02\x03\x04\x05).

A practical approach is to use packet capture tools like tcpdump or Wireshark on the network interface handling NGAP traffic, then filter for NGSetupRequest messages and inspect the RANNodeName IE for invalid characters.

• Use tcpdump to capture NGAP traffic: tcpdump -i <interface> -w ngap_capture.pcap port <NGAP_port>
• Open the capture file in Wireshark and filter for NGSetupRequest messages.
• Inspect the RANNodeName IE field for non-PrintableString bytes or unexpected characters.

Additionally, check free5GC logs for warnings or trace messages indicating rejection or acceptance of malformed PrintableString values, as the vulnerable version improperly accepts invalid data without error.

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Mitigation Strategies

The immediate mitigation step is to apply the patch identified by commit 26205eb01705754b7b902ad6c4b613c96c881e29, which enforces strict validation of PrintableString values according to the X.680 ASN.1 standard.

This patch updates the free5gc/aper component to reject malformed NGAP messages containing invalid PrintableString data, preventing potential crashes or security issues.

If patching immediately is not possible, consider monitoring and filtering NGAP traffic to block or alert on messages with invalid RANNodeName fields to reduce exposure.

It is also recommended to upgrade free5GC to a version that includes this fix or apply the pull request #11 from the free5gc/aper repository that implements the validation.

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Compliance Impact

The vulnerability in Free5GC 4.2.0 involves improper acceptance of non-PrintableString values where the specification mandates PrintableString encoding, leading to potential crashes or bugs. This deviation from the ASN.1 X.680 standard indicates a lack of strict type validation in message processing.

While the CVE description and resources do not explicitly mention compliance with standards such as GDPR or HIPAA, the acceptance of malformed or invalid data could pose risks to system stability and security, which indirectly may affect compliance with regulations that require data integrity and secure processing.

The patch enforces strict validation of PrintableString values according to the X.680 ASN.1 specification, improving adherence to protocol standards and reducing risks of processing invalid data.

However, there is no direct information provided about the impact of this vulnerability on compliance with specific regulations like GDPR or HIPAA.

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