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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-104846?
2 open source packages ship an affected version, including seroval.
| Package | 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.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-104846 being exploited?
There is no known exploitation of CVE-2026-104846 in the wild and no public exploit code.
Sources
Also known as CLSA-2026-1791973750, CLSA-2026-1792286818, GHSA-p6vx-979v-rg4c.