Answer in brief
CVE-2026-126366 records a High severity (CVSS 7.5) vulnerability in msgpack-java JRuby decoder allocates from declared header counts with no cap: 5-byte message forces multi-GiB OOM. The current sources do not mark it as known exploited. The current feed maps msgpack/msgpack-ruby (generic), msgpack (rubygems), msgpack (rubygems). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps msgpack/msgpack-ruby (generic), msgpack (rubygems), msgpack (rubygems). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| msgpack/msgpack-rubygeneric | <1.8.7 | 1.8.7 |
| msgpackrubygems | <=1.8.6 | 1.8.7 |
| msgpackrubygems | >=0 <1.8.7 | 1.8.7 |
Published upstream
Nov 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Nov 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Nov 12, 2026
MessagePack for Ruby is an implementation of the MessagePack binary serialization format. Prior to 1.8.7, the Java-platform msgpack gem for JRuby allocated arrays and byte buffers directly from attacker-controlled array32, str32, and bin32 declared sizes before confirming that corresponding elements or bytes were available. A short MessagePack header could therefore trigger a very large allocation or sustained heap growth when an application decoded untrusted input through MessagePack.unpack or MessagePack::Unpacker, potentially exhausting the shared JVM heap. map32 and declared counts at or above 2^31 did not use the affected allocation behavior. This issue is fixed in version 1.8.7.
Quoted source text, attributed separately from HOL analysis.