Security Digest · Vulnerability record
CVE-2026-104846: Seroval: `fromJSON()` Promise thenable assimilation invokes plugin-produced callables (bypass of GHSA-mv8w-475r-vwqw)
Seroval facilitates JS value stringification, including complex structures beyond JSON.stringify capabilities.
CVSS 9.8 Critical EPSS 0.3% · p27
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.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.3%, percentile 27: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 27% of all scored CVEs (low). 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
seroval(npm) >= 0.12.0, <= 1.6.0, fixed in 1.6.2. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
A fulfilled Promise node deserialized by fromJSON() can trigger unintended invocation of a plugin-produced callable through native ECMAScript thenable assimilation. This bypasses the type-confusion fix in seroval@1.5.3 (GHSA-mv8w-475r-vwqw / CVE-2026-59940) and affects every plugin-capable release from 0.12.0 through the current 1.6.0.
Weakness type: CWE-843.
Product: seroval (npm) · Assigned by: GitHub_M · Published: 2026-10-02
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| npm | seroval | >= 0.12.0, <= 1.6.0 | 1.6.2 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| lxsmnsyc | seroval | >= 0.12.0, < 1.6.2 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 9.8 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| GitHub | 3.1 | 9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
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 none, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.34% probability of exploitation activity in the next 30 days; percentile 27.
Timeline
- — CVE record published by GitHub_M
- — CVE record last updated
- — GitHub-reviewed advisory GHSA-p6vx-979v-rg4c published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-p6vx-979v-rg4c github.com
- CVE.org record CVE-2026-104846 cve.org
- NVD entry CVE-2026-104846 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com