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Security audit

Seamless Looper

Security checks for vulnerabilities and agentic risk

Overview

The skill is a coherent video-looping helper, but its bundled shell script has an unvalidated argument that can execute unintended local commands.

Review this skill before installing. Its purpose is narrow and there is no evidence of hidden persistence or exfiltration, but only use a patched version or pass a simple trusted numeric crossfade value; do not let untrusted text become the third script argument.

A.I.G

Vulnerability Patterns
  • Insecure Skill Coding PracticesFinds exploitable flaws such as hardcoded secrets or command injection
  • Skill Instruction HijackingAlters the agent's session goals or safety constraints when the skill loads
  • Agent Memory PoisoningWrites attacker-controlled rules into memory that affect later sessions
  • Remote Payload Retrieval and ExecutionFetches external code whose behavior can change after review
  • Embedded Malicious CodeShips malicious scripts inside the skill and executes them locally
Findings (1)

T09 · Insecure Skill Coding Practices

Error
Location
scripts/loop.sh:14
Finding

Command Injection Through Unvalidated Crossfade Argument

Content
View full analysis
/dev/null || ! command -v ffprobe &>/dev/null; then echo "ERROR: ffmpeg and ffprobe required. Install with: brew install ffmpeg" exit 1 fi for f in "$SRC_DIR"/*.mp4; do if [ ! -f "$f" ]; then echo "No .mp4 files found in $SRC_DIR" exit 1 fi filename=$(basename "$f") name="${filename%.mp4}" echo "Processing: $filename" dur=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "$f") dur=${dur%.*} if [ -z "$dur" ] || [ "$dur" -lt 2 ]; then echo " Skipping $filename — duration <2s or unknown" continue fi half_dur=$((dur - XFADE)) echo " Duration: ${dur}s | Crossfade: ${XFADE}s | Output: ${name}_looped.mp4" ffmpeg -y -stream_loop 1 -i "$f" -i "$f" \ -filter_complex "[0:v]format=pix_fmts=yuva420p,fade=t=in:st=0:d=0.5:alpha=0[v0];[1:v]format=pix_fmts=yuva420p,fade=t=out:st=${half_dur}:d=${XFADE}:alpha=0[v1];[v0][v1]overlay=0:0:enable='between(t,${half_dur},'$(($half_dur + $XFADE))')'[out]" \ -map "[out]" \ -c:v libx264 -preset fast -crf 18 \ -t "$((dur * 2))" \ ``` ### Technical Analysis The third positional argument is assigned directly to `XFADE` without validating that it is a safe numeric value: ```bash XFADE="${3:-1}" ``` It is subsequently evaluated by Bash arithmetic expansion: ```bash half_dur=$((dur - XFADE)) ``` Bash recursively evaluates variable values used as arithmetic expressions. Arithmetic expressions can interpret variable and array-subscript syntax, and array subscripts may cause embedded command substitutions to be evaluated. Consequently, an attacker-controlled `XFADE` value containing a crafted arithmetic expression can cause a shell command to execute when the ...[truncated 2260 chars]
Remediation
View remediation
&2 exit 1 fi ``` 2. Apply an explicit reasonable upper bound to prevent invalid filters and excessive processing: ```bash if (( XFADE > 30 )); then echo "ERROR: crossfade_seconds must not exceed 30" >&2 exit 1 fi ``` 3. For each input file, verify that the crossfade is smaller than its duration before calculating `half_dur`: ```bash if (( XFADE >= dur )); then echo "Skipping $filename — crossfade must be shorter than the video" >&2 continue fi ``` 4. If fractional crossfade values such as `0.5` must be supported, do not pass them through Bash arithmetic expansion. Validate them with a strict decimal regular expression and perform calculations using a numeric tool such as `awk`, while passing values as data rather than source code: ```bash if [[ ! "$XFADE" =~ ^([0-9]+)(\.[0-9]+)?$ ]]; then echo "ERROR: invalid crossfade duration" >&2 exit 1 fi half_dur=$(awk -v d="$dur" -v x="$XFADE" 'BEGIN { printf "%.6f", d - x }') ``` 5. Reject negative values, exponent notation, shell metacharacters, whitespace, variable names, brackets, and all other non-numeric syntax. 6. Retain quoting around filesystem paths and FFmpeg arguments, and add automated regression tests that pass malicious arithmetic expressions as the third argument and verify that no command is executed. ]]>

SkillSpector

Vulnerability Patterns
  • Rogue AgentSelf-Modification, Session Persistence
  • Prompt InjectionInstruction Override, Hidden Instructions, Exfiltration Commands
  • Data ExfiltrationExternal Transmission, Env Variable Harvesting, File System Enumeration
  • Privilege EscalationExcessive Permissions, Sudo/Root Execution, Credential Access
  • Supply ChainUnpinned Dependencies, External Script Fetching, Obfuscated Code
Findings (1)

Session Persistence

Medium
Category
Rogue Agent
Confidence
60% confidence
Finding

Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.

Content

Scanner excerpt · SKILL.md (reported line 3)May include surrounding context.

md
---
name: seamless-looper
description: Create seamless looping video files with smooth crossfade transitions at the loop junction. Use when asked to loop a video, make a seamless loop, create ambient video loops, crossfade video loops, or loop background footage. Output is visual-only (no audio). Trigger phrases: "loop video", "seamless loop", "video loop", "crossfade loop", "ambient video", "background loop", "loop MP4".
---

# Seamless Looper

Static analysis

No suspicious patterns detected.