From 66b4f6f08abd46af66f85a1d10bf607de7e74634 Mon Sep 17 00:00:00 2001
From: Al Snow <43523+jasnow@users.noreply.github.com>
Date: Fri, 13 Nov 2026 13:40:27 -0500
Subject: [PATCH] One new msgpack advisory

---
 gems/msgpack/CVE-2026-126366.yml | 78 ++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 gems/msgpack/CVE-2026-126366.yml

diff --git a/gems/msgpack/CVE-2026-126366.yml b/gems/msgpack/CVE-2026-126366.yml
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+---
+gem: msgpack
+platform: jruby
+cve: 2026-126366
+ghsa: 73v3-wf97-vpgj
+url: https://nvd.nist.gov/vuln/detail/CVE-2026-126366
+title: msgpack-ruby JRuby decoder makes uncapped header-count
+  allocations; a 5-byte message forces multi-GiB OOM
+date: 2026-11-12
+description: |
+  ### Summary
+
+  The **JRuby** implementation of msgpack (`msgpack` gem,
+  `java` platform — pure Java decoder under `ext/java/`) sizes containers
+  directly from the element count written in the message header, with
+  **no cap at all**: no equivalent of the C unpacker's `SHRT_MAX` clamp
+  (since 1.7.3) and none of the buffered-bytes cap that commit c8d42d8
+  added for CRuby in 1.8.6. A single 5-byte message decides how much
+  memory a JVM process tries to allocate:
+
+  * `array32` header declaring `0x7FFFFFFF` elements → `new
+    IRubyObject[0x7FFFFFFF]` (~8 GiB of reference slots) attempted
+    immediately → `java.lang.OutOfMemoryError: Requested array size
+    exceeds VM limit`.
+
+  * Counts *below* the VM's max-array-size but above available heap
+    (e.g. 5×10⁸ with a 512 MiB heap) produce a **real allocation attempt**
+    — `OutOfMemoryError: Java heap space` — the JVM genuinely tries to
+    take the memory before failing.
+
+  * `str32`/`bin32` headers declaring `0x7FFFFFFF` bytes do the same
+    via `readBytes(size)` → `new byte[size]`.
+
+  * Below the failure threshold there is a **silent band**: one streaming
+    unpacker fed only an `array32` header with count 2×10⁷ (5 wire bytes,
+    zero elements) grows used heap **+78 MiB immediately**, no exception
+    (`each` swallows the underflow), and the footprint stays elevated
+    after `Unpacker#reset` + full GC. Linear in declared count
+    (~4 B/element); nothing bounds it — not delivered bytes, not a
+    per-container cap.
+
+  Only counts ≥ 2³¹ are refused (a clean `MessagePack::UnderflowError`
+  from `getUnsignedInt()`), and only **maps** are safe (`consumeHash`
+  grows per element instead of pre-sizing). Verified on the released
+  gem `msgpack 1.8.6 java`, JRuby 9.4.12 / OpenJDK 25, 2026-10-30 —
+  i.e. **unfixed in the current release**. Proposed fix mirrors
+  c8d42d8: cap initial allocation by bytes actually buffered and
+  grow as data arrives; read strings in bounded chunks instead of
+  allocating the declared length up front.
+
+  ### Impact
+
+  **Type.** Uncontrolled resource consumption driven by *declared* sizes
+  rather than delivered bytes — CWE-770 (Allocation of Resources Without
+  Limits or Throttling), precisely CWE-1325 (Independent Resource Usage
+  Limiting Not Applied). Availability only; no confidentiality/integrity
+  impact, no code execution.
+
+  **Who is impacted.** Any JRuby application that feeds untrusted msgpack
+  to `MessagePack.unpack`/`Unpacker` — the java-platform gem's whole
+  user base (JRuby-based services, log/RPC pipelines, JVM polyglot
+  stacks using this gem). For them: remote OOM of a shared-heap JVM
+  from a 5-byte message, or silent heap spend below the exception band.
+cvss_v3: 7.5
+patched_versions:
+  - ">= 1.8.7"
+related:
+  url:
+    - https://nvd.nist.gov/vuln/detail/CVE-2026-126366
+    - https://rubygems.org/gems/msgpack/versions/1.8.7
+    - https://github.com/msgpack/msgpack-ruby/releases/tag/v1.8.7
+    - https://github.com/msgpack/msgpack-ruby/commit/ca0efc1256c687b428c46dd68ce000ff515d53f2
+    - https://advisories.gitlab.com/gem/msgpack/CVE-2026-126366
+    - https://github.com/msgpack/msgpack-ruby/security/advisories/GHSA-73v3-wf97-vpgj
+    - https://github.com/advisories/GHSA-73v3-wf97-vpgj
+notes: |
+  - cvss_v3 from nvd.nist.gov and GHSA URLs.
+  - gem name is "msgpack" and repo name is "msgpack-ruby".