VulnerabilityPublished 28 Oct 2026

CVE-2026-118666: GraphQL Tools · Shared legacy executor routes one subscription's results to a different caller

Affects @graphql-tools/executor-legacy-wsSource GCVE Database

Authoritative record:CVE-2026-118666· Medium 6.0

Not known to be exploited · CVSS 6.0 Medium : upgrade to 1.1.36 when convenient.

Data as of 28 Oct 2026, 22:12 UTC

CVSS 4.0 base score

6.0Medium

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

Patch: Available – fixed in 1.1.36

CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: High
Attack Requirements: Present
Privileges Required: Low
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 @graphql-tools/executor-legacy-ws to 1.1.36.

Affected software

Product	Affected	Fixed in
npm@graphql-tools/executor-legacy-ws	Affected <1.1.36	Fixed in 1.1.36

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

Description

# Cross-tenant subscription data leak in `@graphql-tools/executor-legacy-ws`: a shared `websocket.onmessage` is replaced on every `subscribe()`, and `DATA` frames are delivered without checking the protocol operation id ## Report metadata | Field | Value | | --- | --- | | Package | `@graphql-tools/executor-legacy-ws` (npm, `pkg:npm/%40graphql-tools/executor-legacy-ws`) | | Repository | https://github.com/ardatan/graphql-tools | | Component | `buildWSLegacyExecutor` → the returned executor's `subscribe(observer)` / `websocket.onmessage` handler | | Vulnerability class | Cross-tenant data leak (subscription results delivered to the wrong caller) | | Verified against | Source at `b5d1c36ebb8ed3868260ffee5bbcbb423ad5c1f1` (package version 1.1.33); published npm tarball `1.1.33` with matching source at `d304214db06e8a4ce9cb41138f199e3bc6ed36f2`; the same behaviour also reproduces on the current release `1.1.35` | | API surface | Public documented API (`buildWSLegacyExecutor`) | | Affected in default configuration | Yes — `ensureWebsocket()` reuses an already-`OPEN` socket (`index.ts:35-42`), and the socket has a single mutable `onmessage` property (`index.ts:113`). No single-operation-only restriction is documented, and the return type is the general reusable `DisposableExecutor` (`packages/utils/src/executor.ts:34-57`) | Affected version range: the range recorded for this finding is `<= 1.1.33`, but that is understated — the same proof of concept reproduces on `1.1.35`, and a byte diff of the built CJS output between `1.1.33` and `1.1.35` shows only one unrelated change (`rejectUnauthorized`). ## Summary `buildWSLegacyExecutor` keeps one WebSocket in closure state and installs the message handler by assigning to the socket's single `websocket.onmessage` property inside `subscribe()`. Every new subscription therefore overwrites the previous subscriber's handler, and the handler's `case LEGACY_WS.DATA` branch calls `observer.next(data.payload)` without ever comparing `data.id` to the operation id that this subscription created at line 103 and sent with `START` at line 123. When one executor instance is reused for overlapping subscriptions, the most recent caller receives payloads belonging to the earlier caller, and the earlier caller receives nothing. In a consuming application, the tainted input is an ordinary, correctly-tagged `DATA` frame emitted by the legitimate downstream server for the victim's operation. The attacker does not need to control or compromise that server; they only need to be able to start their own subscription through the same shared executor while the victim's subscription is active — the natural shape of a gateway, stitched schema, or any service that builds a remote executor once and reuses it per request. The surrounding code shows the inconsistency: - `packages/loaders/url/src/index.ts:262-295` (in-repo `UrlLoader` wrapper) → constructs a fresh legacy executor inside each request, so that caller avoids the shared state. - `buildWSLegacyExecutor`'s returned executor, reused across callers → **unsafe: shared `onmessage` overwritten at line 113, `DATA` dispatched without an id check at lines 145-147**. - `packages/loaders/url/src/index.ts:172-182` → also a production caller of the legacy executor; safe only insofar as the wrapper above rebuilds the executor per request, not because of any check in the executor itself. ## Impact A user of a service that shares one legacy executor receives another user's private GraphQL subscription payloads verbatim, with the victim's authorization context, without ever having been authorized for that operation. The victim is simultaneously starved: their own iterator stops receiving the events they subscribed to, because their handler has been detached. Without this bug, the attacker's observer would receive only results for their own operation — and in this implementation, no result at all, since their operation is never `START`ed after `CONNECTION_ACK` has already fired. The new capability is therefore reading data the attacker could not otherwise obtain by any request they are permitted to make, plus a denial of the victim's subscription stream. Scoring note: no CVSS vector was computed for this finding, because exploitability depends on the consuming application's data flow — specifically whether one executor instance is shared across mutually untrusted callers. Consumers that construct a new executor per operation (as the in-repo `UrlLoader` wrapper does at `packages/loaders/url/src/index.ts:262-295`) are not affected by the cross-caller leak. The set of affected downstream consumers has not been enumerated: **unknown**. ## Preconditions 1. One executor value returned by `buildWSLegacyExecutor` is reused rather than constructing a new executor per operation. This is the normal use of an `Executor`: the contract is invoked once per `ExecutionRequest`, the code explicitly reuses an `OPEN` socket, and the returned value holds `Symbol.disp

CWE-200Exposure of Sensitive Information to an Unauthorized Actor (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #20OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design · Separation of Privilege
Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
OWASP Cheat Sheets
Error Handling (opens in a new tab)
Logging (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.4 (opens in a new tab)
V14.3.3 (opens in a new tab)
V7.3.3 (opens in a new tab)
Attack patterns
Subverting Environment Variable Values (opens in a new tab)
ICMP Echo Request Ping (opens in a new tab)
TCP SYN Scan (opens in a new tab)
Enumerate Mail Exchange (MX) Records (opens in a new tab)
DNS Zone Transfers (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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What to do

Affected software

Description

WeaknessesCWE-200

Technical details

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