KEVWire

Security intelligence, with context.

Response snapshot Oct 27, 2026, 02:52 UTC

Back to the wire
Permalink
VulnerabilityCVE-2026-75507

GraphQL-core: Denial of service via quadratic complexity in the OverlappingFieldsCanBeMerged validation rule

The `OverlappingFieldsCanBeMerged` validation rule can be driven into quadratic — and in the worst case `O(n²·m²)` — running time by a small, highly compressible query. A single 364 KB document can occupy one CPU core for over five minutes during *validation*, before any resolver runs.

Published Updated

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.6% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: graphql-core: 3.2.12; graphql-core: 3.3.0rc1. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-vj8h-fx38-h3vc (opens a new tab)

What happened

### Summary

The `OverlappingFieldsCanBeMerged` validation rule can be driven into quadratic — and in the worst case `O(n²·m²)` — running time by a small, highly compressible query. A single 364 KB document can occupy one CPU core for over five minutes during *validation*, before any resolver runs. Because the rule is part of `specified_rules` and therefore enabled by default, every GraphQL-core based server is affected at default settings.

### Details

`OverlappingFieldsCanBeMerged` compares every pair of fields that share a response name and recurses into their sub-selections. The memoization added for CVE-2023-26144 (`GHSA-9pv7-vfvm-6vr7`) is keyed by **named fragment** identity, so it does not cover this path: inline fragments are flattened into the parent selection set before the cache is consulted, and therefore every pair is re-compared from scratch at every nesting level.

Continue reading

Repeating an inline fragment that selects the same response name at two nesting levels multiplies the two effects. There was no comparison budget and no validation timeout, so the rule ran to completion regardless of cost.

The cost is incurred in the **validation phase**, which is what makes this hard to defend against from outside the library: query-depth limiters, complexity analyzers and cost estimators all operate on the parsed document *after* validation, and the malicious document is trivially shallow (depth 3, complexity 1).

The payload is also one short string repeated many times, so it compresses to a few kilobytes and slips past body-size limits and WAF inspection that only see the compressed request.

### Proof of concept

```python import time from graphql import build_schema, parse, validate

schema = build_schema( "type Query { field: Node } type Node { f: Node, g: Node, x: String }" )

def gen(n: int, m: int) -> str: inner = " ".join(["... on Node { x }"] * m) outer = " ".join([f"... on Node {{ f {{ {inner} }} }}"] * n) return f"{{ field {{ {outer} }} }}"

query = gen(200, 100) # 364 KB, gzips to a few KB document = parse(query) start = time.perf_counter() validate(schema, document) # returns no errors — it just burns CPU print(f"{(time.perf_counter() - start):.0f}s") ```

Measured on GraphQL-core 3.2.8 / CPython 3.12 / Linux x86_64:

| n | m | query size | validation time | |---|---|---|---| | 20 | 20 | 7.6 KB | 0.16 s | | 50 | 50 | 46 KB | 5.2 s | | 100 | 100 | 182 KB | 81 s | | 200 | 100 | 364 KB | **319 s** |

Doubling `n` at fixed `m` quadruples the time, as expected for a quadratic outer loop driving a quadratic inner walk.

### Impact

Denial of service. One request pins one worker process for minutes; because CPython holds the GIL for this pure-CPU work, a handful of concurrent requests can saturate a typical multi-worker deployment. No authentication is required, and no data is disclosed or modified.

### Patches

Fixed in **3.2.12** and **3.3.0rc1**.

Validation now enforces a per-document comparison budget. Once `MAX_FIELD_COMPARISONS` (default `250_000`) pairwise comparisons have been made, the rule aborts and reports a `GraphQLError` instead of running to completion:

> Query is too complex to validate for overlapping fields: exceeded 250000 field > comparisons. Validation was aborted.

The default is far above what any realistic query reaches. It is a module-level constant and can be raised or lowered:

```python from graphql.validation.rules import overlapping_fields_can_be_merged

overlapping_fields_can_be_merged.MAX_FIELD_COMPARISONS = 1_000_000 ```

Note the behaviour change: a pathological query that previously validated — slowly — now produces a validation error.

### Workarounds

If you cannot upgrade, reject oversized documents before they reach `validate()`. Note that a request body-size limit must be applied to the **decompressed** body to be effective here, since the payload is highly compressible. Removing `OverlappingFieldsCanBeMergedRule` from the rule set is *not* a safe workaround: it is a correctness rule required by the specification.

A body-size limit remains worthwhile after upgrading — the comparison budget bounds this specific rule, not overall request cost.

### Credits

Reported by @BZHunt, who also reviewed the fixes before release. In memory of ZaX, who was the driving force behind this discovery.

Independently found and diagnosed by @bcmyguest, who also proposed a fix.

Affected package ranges reported by GitHub: graphql-core: >= 3.0.0, < 3.2.12 graphql-core: >= 3.3.0a1, < 3.3.0rc1

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.6%

Scored Percentile 48.4%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-vj8h-fx38-h3vc (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vj8h-fx38-h3vc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-75507 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  13. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  14. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-75507, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 23). GraphQL-core: Denial of service via quadratic complexity in the OverlappingFieldsCanBeMerged validation rule (CVE-2026-75507). https://kevwire.com/record/CVE-2026-75507

MLA

"GraphQL-core: Denial of service via quadratic complexity in the OverlappingFieldsCanBeMerged validation rule (CVE-2026-75507)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-75507.

Chicago

KEVWire. "GraphQL-core: Denial of service via quadratic complexity in the OverlappingFieldsCanBeMerged validation rule (CVE-2026-75507)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-75507.

Evidence summary (plain text)

GraphQL-core: Denial of service via quadratic complexity in the OverlappingFieldsCanBeMerged validation rule (Oct 22, 2026).
The `OverlappingFieldsCanBeMerged` validation rule can be driven into quadratic — and
in the worst case `O(n²·m²)` — running time by a small, highly compressible query. A
single 364 KB document can occupy one CPU core for over five minutes during
*validation*, before any resolver runs. Because the rule is part of `specified_rules`
and therefore enabled by default, every GraphQL-core based server is affected at
default settings.

`OverlappingFieldsCanBeMerged` compares every pair of fields that share a response
name and recurses into their sub-selections. The memoization added for
CVE-2023-26144 (`GHSA-9pv7-vfvm-6vr7`) is keyed by **named fragment** identity, so it
does not cover this path: inline fragments are flattened into the parent selection
set before the cache is consulted, and therefore every pair is re-compared from
scratch at every nesting level.
CVSS 7.5 (version 3.1; evidence as of Oct 23, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-75507).
EPSS 0.6% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-75507&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-vj8h-fx38-h3vc: https://github.com/advisories/GHSA-vj8h-fx38-h3vc
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo1MTozMFrOAAf0Mg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0OToxMlrOAAf0LQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NzoxN1rOAAf0Kg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTozNlrOAAf0Jw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTowNVrOAAf0JQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0Mzo0NVrOAAf0Iw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0MzozMVrOAAf0Ig%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozNTowMVrOAAZRcw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozMDoyN1rOAAY_5Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODoyOTowNVrOAAfz8g%3D%3D
NVD CVE-2026-75507: https://nvd.nist.gov/vuln/detail/CVE-2026-75507
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=8500
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-75507&date=2026-10-26
Record ID: CVE-2026-75507.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

Your account

Email alerts

Email alerts are not available yet. To follow your stack today, use its RSS feed, which honors your filters, or connect an AI agent through the API.

Suggest an improvement

Ideas, missing sources, corrections, and bugs are all welcome. No account needed. Suggestions are reviewed by a person before anything changes.

Record details

Record detail