CVE-2026-75507VulnerabilityPublished 23 Oct 2026Updated 29 Oct 2026

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

Affects schemathesisSource GCVE Database

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Authoritative record:CVE-2026-75507· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 4.26.0 soon.

Data as of 30 Oct 2026, 07:16 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	7.5

EPSS: 0.6% chance of exploitation in 30 days – higher than 48% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.26.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade schemathesis to 4.26.0.

Affected software

Product	Affected	Fixed in
Homebrewschemathesis`pkg:brew/schemathesis`Other threats	Affected >=3.17.2 <4.26.0	Fixed in 4.26.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade GraphQL-core to version 3.2.12 or later, or 3.3.0rc1 or later, where a comparison budget limits validation cost and aborts excessive queries. If upgrading is not possible, implement request body-size limits on the decompressed request to reject oversized documents before validation. Do not remove the OverlappingFieldsCanBeMerged rule, as it is required for specification compliance. The default comparison budget is high enough to allow legitimate queries while preventing pathological ones.

Description

A denial of service vulnerability exists in GraphQL-core's OverlappingFieldsCanBeMerged validation rule, which can be exploited by a crafted query causing quadratic to worst-case O(n²·m²) validation time. This can exhaust CPU resources for minutes on a single core during validation, without requiring authentication or exposing data. The issue affects default settings of GraphQL-core based servers. The vulnerability is fixed in versions 3.2.12 and 3.3.0rc1 by enforcing a comparison budget that aborts validation on excessive complexity.

Impact

An attacker can cause a denial of service by sending a specially crafted GraphQL query that consumes excessive CPU resources during the validation phase, potentially saturating server worker processes. No authentication is required, and no data confidentiality or integrity is affected. The vulnerability can degrade availability by exhausting CPU cores for minutes per request.

Summary

The OverlappingFieldsCanBeMerged validation rule in GraphQL-core compares every pair of fields sharing a response name and recurses into sub-selections, resulting in quadratic complexity. Inline fragments are flattened before memoization, causing repeated re-comparisons at each nesting level. This leads to a worst-case O(n²·m²) runtime for certain crafted queries, which are shallow and highly compressible, evading typical depth or complexity limiters and WAF inspection. The vulnerability allows an attacker to cause high CPU usage during the validation phase, effectively a denial of service. The issue was fixed by introducing a per-document comparison budget (default 250,000 comparisons) that aborts validation with an error if exceeded. The fix is included in GraphQL-core versions 3.2.12 and 3.3.0rc1.

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Description

AI analysisMachine-generated, updated 30 Oct 2026, 07:16 UTC

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