# CVE-2026-93753: deepmerge through 4.3.1 Prototype Poisoning via mergeObject

> Attackers can inject properties into object prototypes via merge operations, potentially leading to code execution or privilege escalation in applications using the library.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Sep 2026
- **Updated:** 24 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-93753, GHSA-gcqx-w48m-w2h4, MINI-3hrf-5869-gx4x, MINI-3qcp-6vx6-5xc8, MINI-c3jq-hxm4-v8xr, MINI-cj6w-h26h-g657, MINI-cqc8-f9wj-82mr, MINI-qpxg-f4g5-mvv5, UBUNTU-CVE-2026-93753, openSUSE-SU-2026:12285-1

## What is CVE-2026-93753?

CVE-2026-93753 is a high-severity vulnerability in TehShrike deepmerge, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

deepmerge through 4.3.1 contains a prototype poisoning vulnerability in the mergeObject() function that fails to properly validate keys being written to target objects. Attackers can supply malicious source objects in merge operations to inject attacker-controlled properties into the returned object's prototype, causing applications to inherit unintended values when accessing properties without own-property checks.

Weakness: CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-93753?

2 open source packages ship an affected version, including deepmerge.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `deepmerge` | npm | From 4.2.0 to 4.3.1 | None |
| `deepmerge` | npm | From 4.2.0 to 4.3.1 | None |
| `golang-github-prometheus-prometheus` | openSUSE:Tumbleweed | All versions | 3.15.0-2.1 |

## How do I fix CVE-2026-93753?

Upgrade to a fixed version.

## Is CVE-2026-93753 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-93753 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93753 and fix it if it is affected.

What it is: CVE-2026-93753 is a high-severity vulnerability in TehShrike deepmerge, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-93753 exists.

Affected packages and fixed versions:
- deepmerge (npm): affected from 4.2.0 up to 4.3.1; no fix listed
- deepmerge (npm): affected from 4.2.0 up to 4.3.1; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-93753/ (Markdown: https://insights.sbomify.com/CVE-2026-93753/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93753
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93753
- OSV: https://osv.dev/vulnerability/CVE-2026-93753

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93753/
Summaries are generated and may contain mistakes; the official description above is the record.