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PIIMiddleware "Ip" Type Fails To Detect IPv6 Addresses, Allowing PII Leakage

The PIIMiddleware with type="ip" only compiles an IPv4 regex, so IPv6 addresses are not redacted or blocked, causing silent PII leakage to the model.

highConfidence 95%Langchain Affected V1.3.16

Origin Analysis

In langchain/agents/middleware/_redaction.py, detect_ip() uses only an IPv4 pattern (`\b(?:[0-9]{1,3}\.){3}[0-9]{1,3}\b`) despite its docstring claiming IPv4 or IPv6 support. The validation helper `ipaddress.ip_address()` already accepts both families, but no IPv6 candidate pattern is ever considered, so IPv6 strings never reach validation.

Run the provided Python code: instantiate PIIMiddleware("ip", strategy="redact") with a message containing an IPv6 address (e.g., "Server IP: 2001:0db8:85a3:0000:0000:8a2e:0370:7334"); observe the address is not redacted. Similarly with strategy="block", no PIIDetectionError is raised.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

Behavior change: IPv4-mapped IPv6 addresses (e.g., ::ffff:192.168.1.1) will now be fully matched and redacted/hashed as a unit, altering previous redaction output and hash digests. This may affect audit logs or hash-based deduplication. Rollback: if necessary, revert to the previous IPv4-only pattern, but this reintroduces the leakage. Test thoroughly with various IPv6 formats, IPv4-mapped addresses, and non-IP colon strings to avoid false positives. The function is stateless, so no concurrency issues, but ensure any cached compiled regexes are versioned appropriately across deployments.