T09 · Insecure Skill Coding Practices
- Location
SKILL.md:42- Finding
Weak Integrity Verification Misrepresented as Tamper-Resistant Logging
- Content
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Vulnerability Details
File Location:
SKILL.md, lines 42–63 and 146–159
Vulnerability Type: Integrity verification weakness and insecure audit-log design
Risk Level: MediumVulnerable Code
text CAN协议用最简单的三列模型解决这个问题：每条数据记录三个信息——它发生的时间（WHEN）、它内容的哈希（WHERE）、你给它起的名字（WHAT）。这三列完全由你控制，append-only追加写入，任何篡改都会导致哈希不匹配。text - 日志采用append-only设计，只增不删不改 - 任何对历史记录的修改都会导致哈希校验失败bash # 计算内容哈希 echo -n "your-data-content" | sha256sum # 记录三列 echo "1742428800000 a7f3b2c1d4e5 客户名单-2024Q1" >> can.logbash # 重新计算当前内容的哈希 current_hash=$(echo -n "your-data-content" | sha256sum | cut -c1-12) # 在日志中查找 grep "$current_hash" can.log # 命中即表示内容与打戳时一致Technical Analysis
The documented implementation does not provide an append-only or tamper-evident audit log. Shell redirection with
>>appends a record during that operation, but it does not prevent a user or process with write permission from modifying, deleting, truncating, reordering, or replacing previous records. No hash chain, digital signature, HMAC, authenticated checkpoint, or separately protected integrity root binds the log history together.The verification procedure also truncates SHA-256 to 12 hexadecimal characters, providing only 48 bits of hash space, and uses unstructured substring matching through
grep. A match establishes only that the selected hash prefix occurs somewhere in the file. It does not establish that the hash belongs to the expected timestamp and name, that the corresponding record is unique, or that the log history is authentic.The log contains the asserted digest but does not authenticate it. An attacker who can alter both protected data and
can.logcan calculate a digest for replacement content and update or append a corresponding record. The documented verification then reports a successful match.Attack Path
- An attacker or compromised process obtains write access to the protected data and
can.log. - The attacker changes the protect ...[truncated 1336 chars]
- An attacker or compromised process obtains write access to the protected data and
- Remediation
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Remediation Suggestions
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Use complete digests
- Store and compare the full 256-bit SHA-256 digest.
- Do not use a 12-character prefix for security-sensitive integrity decisions.
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Parse exact structured records
- Use a well-defined format such as JSON Lines.
- Compare the expected digest against the exact record and fields rather than using substring-based
grep. - Validate timestamp, digest, name, field count, encoding, and record uniqueness.
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Cryptographically bind the history
- Include the preceding record's full hash in every new record.
- Compute each record hash over all canonicalized fields, including the preceding hash.
- Verify the complete chain from a trusted root before accepting a record.
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Authenticate records or checkpoints
- Protect records or periodic chain roots with an HMAC whose key is inaccessible to log writers, or with digital signatures.
- Store authenticated roots in a separate, access-controlled location.
- Use an external timestamp or transparency service where independent time assurance is required.
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Strengthen storage controls
- Separate data-writing and audit-verification privileges.
- Use operating-system append-only controls or a dedicated immutable/WORM log service where supported.
- Treat read-only permissions and version control only as defense-in-depth, not as cryptographic tamper protection.
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Correct the security claims
- Describe the current file as append-oriented rather than append-only or tamper-proof.
- State explicitly that a plain hash log cannot detect alterations made by an actor who can update both the data and its recorded digest.
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Add adversarial tests
- Test record deletion, truncation, reordering, duplicate digest prefixes, altered names and timestamps, and coordinated replacement of data and log entries.
- Require verification to fail for every unauthorized history modification.
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