CWE-1286: Improper Validation of Syntactic Correctness of Input
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.
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Overview
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.
Real-world CVEs
83 recorded CVEs are caused by CWE-1286 (Improper Validation of Syntactic Correctness of Input). The highest-severity and most recent are shown first. 34 new CWE-1286 CVEs have been recorded so far in 2026 (21 in 2025).
- CVE-2026-102084
Junos OS: SRX Series: In an ADVPN scenario a malformed message from a peer causes Remote Code Execution
Critical · CVSS 9.2 · EPSS 42th2026-10-14 - CVE-2026-87080
Net::IDN::Punycode::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode
Critical · CVSS 9.1 · EPSS 32th2026-09-22