Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
The msgpack5 npm package is vulnerable in versions before 6.1.0. The reserved MessagePack byte 0xc1 is wrongly treated as incomplete input, so a stream decoder keeps buffering all later data while waiting for bytes that can never complete a valid value. An attacker who can send such a stream to an application using the decoder could cause memory exhaustion. Upgrade to msgpack5 version 6.1.0 or later, which rejects 0xc1 as invalid and releases buffered input after unrecoverable errors.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 5.9 | Medium | 3.1 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0039, the 33rd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 13:33 UTC First seen by agentprime
- 31 Oct 2026, 13:33 UTC Confirmed by OSV