An Improper Validation of Syntactic Correctness of Input vulnerability in the VPN daemon of Juniper Networks Junos OS on SRX Series allows an authenticated, network-based attacker to take complete control of the device.
If an SRX device configured for AutoDiscovery VPN (ADVPN) receives a message from a peer that contains one or more specifically malformed attributes, this will cause a buffer overflow, which can allow remote code execution and therefore allow an attacker to take complete control of the device. To be able to carry out this attack an attacker must either have acquired the shared secret to impersonate a peer or have compromised an existing one, so this attack is considerably difficult.
This issue affects Junos OS on SRX Series:
- All versions before 23.2R2-S7.7;
- from 23.4 before 23.4R2-S7;
- from 24.2 before 24.2R2-S4;
- from 24.4 before 24.4R2-S3;
- from 25.2 before 25.2R2;
- from 25.4 before 25.4R1-S3.
Weakness
The product receives input that is expected to be well-formed - i.e., to comply with a certain syntax - but it does not validate or incorrectly validates that the input complies with the syntax.
Extended Description
Often, complex inputs are expected to follow a particular syntax, which is either assumed by the input itself, or declared within metadata such as headers. The syntax could be for data exchange formats, markup languages, or even programming languages. When untrusted input is not properly validated for the expected syntax, attackers could cause parsing failures, trigger unexpected errors, or expose latent vulnerabilities that might not be directly exploitable if the input had conformed to the syntax.
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.