CVE-2026-77415: JSONata vulnerable to Arbitrary Code Execution via crafted JSONata expressions

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.9%, percentile 59: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 59% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes jsonata (npm) >= 2.0.0, < 2.2.1, fixed in 2.2.1; jsonata (npm) < 1.8.8, fixed in 1.8.8. Check your lockfile, including transitive dependencies.

What it is

JSONata is a JSON query and transformation language. Prior to 1.8.8 and 2.2.1, crafted JSONata expressions could chain several object-integrity weaknesses to execute arbitrary code. The chain could overwrite $clone to mutate objects through evaluateTransformExpression, expose and deconstruct JSONata functions or lambdas through $merge., replace proc.arguments.forEach used by applyProcedure, and forge internal lambda state. These primitives allowed an attacker to reach prototype getters, prototype and constructor access, and process.getBuiltinModule with childprocess, executing code with the privileges of the host process. This issue is fixed in versions 1.8.8 and 2.2.1.

From the GitHub advisory

Before JSONata 2.2.1 and 1.8.8 it was possible to execute arbitrary code with crafted expressions, due to: - overwriting $clone allowing mutation of objects via transforms (see evaluateTransformExpression) - it being possible to destruct jsonata functions/lambdas (e.g. $merge.) - applyProcedure using proc.arguments.forEach and not Array.prototype.forEach

Which could be chained to execute arbitrary code.

This was fixed with:

- https://github.com/jsonata-js/jsonata/pull/799 (https://github.com/jsonata-js/jsonata/pull/799/changes#diff-de23c1b6e199d0e59406a284aae5fa7be63fcbbff706829913dba73dcdeb061cL1673-R1673) - https://github.com/jsonata-js/jsonata/pull/800 - https://github.com/jsonata-js/jsonata/pull/802

Which are included in the 2.2.1 release. Fixes were then back-ported to the 1.8.8 release.

Weakness type: CWE-94.

Product: jsonata (npm) · Assigned by: GitHub_M · Published: 2026-08-21

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.89% probability of exploitation activity in the next 30 days; percentile 59.

Timeline

• 2026-08-21 — CVE record published by GitHub_M
• 2026-08-21 — GitHub-reviewed advisory GHSA-66mm-25pp-rfff published (critical)
• 2026-08-25 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-66mm-25pp-rfff github.com
2. CVE.org record CVE-2026-77415 cve.org
3. NVD entry CVE-2026-77415 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
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