# CVE-2026-104846: Seroval: `fromJSON()` Promise thenable assimilation invokes plugin-produced callables (bypass of CVE-2026-59940)

> Attacker-controlled JSON can trigger unexpected code execution in applications using Seroval's fromJSON method with plugins, bypassing previous security fixes.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Oct 2026
- **Updated:** 5 Oct 2026
- **Also known as:** CLSA-2026-1791973750, CLSA-2026-1792286818, GHSA-p6vx-979v-rg4c

## What is CVE-2026-104846?

CVE-2026-104846 is a critical code injection vulnerability in lxsmnsyc seroval, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Seroval facilitates JS value stringification, including complex structures beyond JSON.stringify capabilities. From 0.12.0 until 1.6.2, fromJSON deserialization of a fulfilled Promise control node can pass a plugin-produced callable-bearing thenable to a native Promise resolver. ECMAScript thenable assimilation then invokes the callable unexpectedly, allowing attacker-controlled JSON to trigger code in applications using plugin-capable Seroval releases. This path bypasses the Promise resolver type-confusion remediation in version 1.5.3 for CVE-2026-59940 because the unexpected invocation occurs through native Promise settlement after the referenced value is deserialized. This issue is fixed in version 1.6.2.

Weakness: CWE-843 (Access of Resource Using Incompatible Type)

## Which versions are affected by CVE-2026-104846?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `seroval` | npm | From 0.12.0 | 1.6.2 |
| `seroval` | npm | From 0.12.0 | 1.6.2 |

## How do I fix CVE-2026-104846?

Upgrade seroval to 1.6.2 or later.

## Is CVE-2026-104846 being exploited?

There is no known exploitation of CVE-2026-104846 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-104846 and fix it if it is affected.

What it is: CVE-2026-104846 is a critical code injection vulnerability in lxsmnsyc seroval, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-104846 in the wild and no public exploit code.

Affected packages and fixed versions:
- seroval (npm): affected from 0.12.0; fixed in 1.6.2
- seroval (npm): affected from 0.12.0; fixed in 1.6.2

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-2026-104846/ (Markdown: https://insights.sbomify.com/CVE-2026-104846/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-104846
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-104846
- OSV: https://osv.dev/vulnerability/CVE-2026-104846

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-104846/
Summaries are generated and may contain mistakes; the official description above is the record.