CVE-2023-36839

An Improper Validation of Specified Quantity in Input vulnerability in the Layer-2 control protocols daemon (l2cpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated adjacent attacker who sends specific LLDP packets to cause a Denial of Service(DoS).

This issue occurs when specific LLDP packets are received and telemetry polling is being done on the device. The impact of the l2cpd crash is reinitialization of STP protocols (RSTP, MSTP or VSTP), and MVRP and ERP. Also, if any services depend on LLDP state (like PoE or VoIP device recognition), then these will also be affected.

This issue affects:

Juniper Networks Junos OS

• All versions prior to 20.4R3-S8;
• 21.1 version 21.1R1 and later versions;
• 21.2 versions prior to 21.2R3-S5;
• 21.3 versions prior to 21.3R3-S4;
• 21.4 versions prior to 21.4R3-S3;
• 22.1 versions prior to 22.1R3-S2;
• 22.2 versions prior to 22.2R3;
• 22.3 versions prior to 22.3R2-S2;
• 22.4 versions prior to 22.4R2;

Juniper Networks Junos OS Evolved

• All versions prior to 20.4R3-S8-EVO;
• 21.1 version 21.1R1-EVO and later versions;
• 21.2 versions prior to 21.2R3-S5-EVO;
• 21.3 versions prior to 21.3R3-S4-EVO;
• 21.4 versions prior to 21.4R3-S3-EVO;
• 22.1 versions prior to 22.1R3-S2-EVO;
• 22.2 versions prior to 22.2R3-EVO;
• 22.3 versions prior to 22.3R2-S2-EVO;
• 22.4 versions prior to 22.4R1-S1-EVO;

Weakness

The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.

Affected Software

Extended Description

Specified quantities include size, length, frequency, price, rate, number of operations, time, and others. Code may rely on specified quantities to allocate resources, perform calculations, control iteration, etc. When the quantity is not properly validated, then attackers can specify malicious quantities to cause excessive resource allocation, trigger unexpected failures, enable buffer overflows, etc.

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

References

• https://supportportal.juniper.net/JSA73171