Improper Neutralization of Escape, Meta, or Control Sequences
Incomplete Variant
Structure: Simple
Description
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as escape, meta, or control character sequences when they are sent to a downstream component.
As data is parsed, an injected/absent/malformed delimiter may cause the process to take unexpected actions.
Common Consequences 1
Scope: Integrity
Impact: Unexpected State
Potential Mitigations 4
Developers should anticipate that escape, meta and control characters/sequences will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
Phase: Implementation
Strategy: Input Validation
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.
Phase: Implementation
Strategy: Output Encoding
While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')).
Phase: Implementation
Strategy: Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (Incorrect Behavior Order: Validate Before Canonicalize). Make sure that the application does not decode the same input twice (Double Decoding of the Same Data). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Observed Examples 11
CVE-2002-0542The mail program processes special "~" escape sequence even when not in interactive mode.
CVE-2000-0703Setuid program does not filter escape sequences before calling mail program.
CVE-2002-0986Mail function does not filter control characters from arguments, allowing mail message content to be modified.
CVE-2003-0020Multi-channel issue. Terminal escape sequences not filtered from log files.
CVE-2003-0083Multi-channel issue. Terminal escape sequences not filtered from log files.
CVE-2003-0021Terminal escape sequences not filtered by terminals when displaying files.
CVE-2003-0022Terminal escape sequences not filtered by terminals when displaying files.
CVE-2003-0023Terminal escape sequences not filtered by terminals when displaying files.
CVE-2003-0063Terminal escape sequences not filtered by terminals when displaying files.
CVE-2000-0476Terminal escape sequences not filtered by terminals when displaying files.
CVE-2001-1556MFV. (multi-channel). Injection of control characters into log files that allow information hiding when using raw Unix programs to read the files.
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Modes of Introduction
Implementation
Related Weaknesses
Taxonomy Mapping
- PLOVER
- The CERT Oracle Secure Coding Standard for Java (2011)
- Software Fault Patterns