T09 · Insecure Skill Coding Practices
Warning
- Location
- scripts/tail.py:14
- Finding
- Unbounded Input Loading Enables Resource Exhaustion## Vulnerability Details **File Location**: `scripts/tail.py`, lines 14-20 **Vulnerability Type**: Unbounded memory consumption and blocking input **Risk Level**: Medium ```python if args.file: try: lines = open(args.file).readlines() except FileNotFoundError: print(f"Error: File not found: {args.file}", file=sys.stderr) sys.exit(1) else: lines = sys.stdin.readlines() ``` ### Technical Analysis The implementation calls `readlines()` on either the selected file or standard input. Despite only needing the final number of lines requested by the user, it loads the entire input into memory before producing any output. A sufficiently large file can cause excessive memory consumption, process termination, or system degradation. When standard input is used, `sys.stdin.readlines()` also waits for end-of-file, so an unbounded or continuously producing input stream can make the command block indefinitely while its memory usage continues to grow. The file is also opened without a context manager, although resource exhaustion from unbounded reads is the principal security concern. ### Attack Path 1. An attacker creates or identifies a file whose size is large relative to available memory, or supplies a stream that continuously emits data. 2. The attacker causes the tool to process that input, for example by invoking it with the large file path or piping the stream into the command. 3. `readlines()` attempts to retain every line in memory. 4. Memory consumption grows until the process is killed, becomes unresponsive, or adversely affects other processes. For a stream without an end-of-file condition, the tool may never produce output. Exploitation requires the ability to influence the file or standard input processed by the tool. It does not provide privilege escalation or arbitrary code execution. ### Impact Assessment The primary impact is local denial of service against the tool ...[truncated 343 chars]
- Remediation
- ## Remediation Suggestions - For standard input, retain only the requested number of lines with a bounded deque: ```python from collections import deque lines = deque(sys.stdin, maxlen=args.lines) ``` - For regular files, implement bounded reverse reading so that only enough data to recover the requested final lines is loaded. Alternatively, use a well-reviewed tail implementation or invoke a trusted platform API without constructing a shell command. - Open files with a context manager to guarantee closure: ```python with open(args.file, "r", encoding="utf-8", errors="replace") as handle: lines = deque(handle, maxlen=args.lines) ``` - Validate that `args.lines` is non-negative and impose a reasonable upper bound. - Where stdin may be supplied by an untrusted or long-running producer, apply execution timeouts and operating-system memory limits.