yara-rule-authoring

ISSUES FOUND max severity CRITICALSkillSpector Do not install 100 registry trailofbits last scanned 2026-02-08 1 scan

19 findings (15 critical, 3 high, 1 low), mainly command injection, obfuscation, policy violation. Most recent scan 2026-02-08.

Findings19

Critical15

High3

Medium0

Low1

Analyzersstatic llm meta

Second scanner: NVIDIA SkillSpector

VerdictDo not install 100

Score100 / 100

Issues11

CategoriesYARA Match Privilege Escalation analysis-evasion

Version2.12.0 (static)

Independent static run, no language model, over the same files as the Cisco scan above. How the two scanners compare across the whole corpus: Two scanners, one corpus.

What this skill does

Guides authoring of high-quality YARA-X detection rules for malware identification. Use when writing, reviewing, or optimizing YARA rules. Covers naming conventions, string selection, performance optimization, migration from legacy YARA, and false positive reduction. Triggers on: YARA, YARA-X, malware detection, threat hunting, IOC, signature, crx module, dex module.

Package: 16 files, 153 KB
SKILL.md: 3637 words, 12+ sections
Code: Python (2)

SKILL.md covers: YARA-X Rule Authoring · Core Principles · When to Use · When NOT to Use · YARA-X Overview · Platform Considerations · macOS Malware Detection · JavaScript Detection Decision Tree · Essential Toolkit · Rationalizations to Reject · Decision Trees · Is This String Good Enough?

Findings

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: #

scripts/atom_analyzer.py:1

# /// script

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[91m

scripts/atom_analyzer.py:455

print(f"\033[91mYARA-X compilation error in {file_path}:\033[0m {e}", file=sys.stderr)

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[0m

scripts/atom_analyzer.py:455

print(f"\033[91mYARA-X compilation error in {file_path}:\033[0m {e}", file=sys.stderr)

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[1m

scripts/atom_analyzer.py:466

print(f"\n\033[1m{rule_name}\033[0m")

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[0m

scripts/atom_analyzer.py:466

print(f"\n\033[1m{rule_name}\033[0m")

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[91m

scripts/atom_analyzer.py:480

color = "\033[91m"

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[93m

scripts/atom_analyzer.py:482

color = "\033[93m"

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[94m

scripts/atom_analyzer.py:484

color = "\033[94m"

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[0m

scripts/atom_analyzer.py:486

print(f"    {color}{issue.severity.upper()}\033[0m: {issue.message}")

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: #

scripts/yara_lint.py:1

# /// script

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[91m

scripts/yara_lint.py:547

red = "\033[91m"

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[93m

scripts/yara_lint.py:548

yellow = "\033[93m"

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[94m

scripts/yara_lint.py:549

blue = "\033[94m"

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[0m

scripts/yara_lint.py:550

reset = "\033[0m"

Remediation: Review and remove injection attack pattern

CRITICAL INJECTION ATTACK detected by YARA Command Injectionstatic

Detects embedded scripting payloads (JS, VBScript, etc.) in MCP tool descriptions: \033[1m

scripts/yara_lint.py:551

bold = "\033[1m"

Remediation: Review and remove injection attack pattern

HIGH XOR operations often used for obfuscation Obfuscationstatic

Pattern detected: xor

scripts/yara_lint.py:424

# xor without range

Remediation: Remove XOR encoding unless clearly justified

HIGH XOR operations often used for obfuscation Obfuscationstatic

Pattern detected: xor

scripts/yara_lint.py:425

if "xor" in modifiers and not any("xor(" in str(m) for m in modifiers):

Remediation: Remove XOR encoding unless clearly justified

HIGH XOR operations often used for obfuscation Obfuscationstatic

Pattern detected: xor

scripts/yara_lint.py:430

message=f"String {string_id} uses 'xor' without range; generates 255 patterns",

Remediation: Remove XOR encoding unless clearly justified

LOW Skill does not specify a license Policy Violationstatic

Skill manifest does not include a 'license' field. Specifying a license helps users understand usage terms.

SKILL.md

Remediation: Add 'license' field to SKILL.md frontmatter (e.g., MIT, Apache-2.0)

What is in the package

File	Kind	Size
`SKILL.md`	doc	26 KB
`examples/MAL_Mac_ProtonRAT_Jan25.yar`	other	3.4 KB
`examples/MAL_NPM_SupplyChain_Jan25.yar`	other	5.7 KB
`examples/MAL_Win_Remcos_Jan25.yar`	other	3.3 KB
`examples/SUSP_CRX_SuspiciousPermissions.yar`	other	4.4 KB
`examples/SUSP_JS_Obfuscation_Jan25.yar`	other	6.0 KB
`references/crx-module.md`	doc	6.5 KB
`references/dex-module.md`	doc	10 KB
`references/performance.md`	doc	8.0 KB
`references/strings.md`	doc	11 KB
`references/style-guide.md`	doc	7.9 KB
`references/testing.md`	doc	13 KB
`scripts/atom_analyzer.py`	script	15 KB
`scripts/pyproject.toml`	config	553 B
`scripts/yara_lint.py`	script	19 KB
`workflows/rule-development.md`	doc	13 KB

External hosts referenced

github.com objective-see.org developer.chrome.com www.elastic.co www.nist.gov www.virustotal.com yara-ci.cloud.virustotal.com yaradbg.dev analysis-report-url.com blog.malwarebytes.com blog.phylum.io stairwell.com www.veracode.com yara.readthedocs.io

Hostnames that appear in the skill's files. Referencing a host is not a finding; compare against the findings above and the skill's stated purpose.

Package contents recorded 2026-10-22 at commit a50696e20581. The scan above ran against the version current at scan time; the two can differ if the skill has since been updated.

What we checked

Static analyzer. Pattern rules over SKILL.md and bundled files: known-bad commands, exfiltration URLs, secrets, obfuscation.
Llm analyzer. A language model reads the skill and reports intent-level issues the rules cannot express.
Meta analyzer. A second model pass that validates, deduplicates and re-scores the other analyzers' findings.

What we did not check

Runtime behaviour. The skill was not executed; findings come from reading its files.
Anything fetched at install or run time, including remote scripts, package dependencies, and URLs the skill tells the agent to open.
Content the analyzers cannot read: images, binaries, and some non-English text.
Known scanner bypass classes. See the methodology and limitations page.

Sources

Repository: https://github.com/trailofbits/skills
Raw scan result: plugins-yara-authoring-skills-yara-rule-authoring-scan.json
Badge for your README: ![skillscan.io](https://skillscan.io/badge/trailofbits-yara-rule-authoring.svg)
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