Vulnerability in MessagePack (CVE-2026-48510)
Summary
Vulnerability in MessagePack (CVE-2026-48510). Risk of unauthorized operations or information disclosure. Exploitable via Lz4Block. Mitigation: upgrade to 3.1.7 or later.
Original description
The description as published by the source.
Summary
When MessagePack-CSharp decompresses Lz4Block or Lz4BlockArray payloads, it reads declared uncompressed lengths from the wire and allocates output buffers based on those lengths before validating that the compressed data is valid or that the declared expansion is reasonable.
A small payload can claim a very large uncompressed length and force a large allocation before LZ4 decoding begins.
Impact
Applications are affected when they deserialize attacker-controlled MessagePack payloads with MessagePackCompression.Lz4Block or MessagePackCompression.Lz4BlockArray enabled.
In the Lz4Block case, an attacker-controlled integer is used to request the destination span. In the Lz4BlockArray case, per-block uncompressed lengths and their aggregate can be attacker-controlled. Without a cap, the declared output size can be disproportionate to the input size, producing out-of-memory exceptions, process termination on constrained hosts, or severe memory pressure.
This advisory is about unbounded allocation from declared decompressed sizes. It is separate from the LZ4 source-buffer over-read issue, which concerns unsafe decoder reads beyond the compressed input buffer.
Affected components
- Package:
MessagePack - Feature: LZ4 compressed MessagePack payloads
- APIs:
MessagePackSerializerwithWithCompression(MessagePackCompression.Lz4Block)orWithCompression(MessagePackCompression.Lz4BlockArray) - Internal routine: `MessagePackSerializer.TryDecompr…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-48510 has been found in MessagePack.
Attackers can target a specific entry point like Lz4Block over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade MessagePack to 3.1.7 or later.
If unsure, ask your IT team or search "MessagePack CVE-2026-48510" on the vendor's site.
CVE-2026-48510 (MessagePack) — CWE-409 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Lz4Block / Lz4BlockArray / MessagePackCompression.Lz4Block / MessagePackCompression.Lz4BlockArray
Patched: 3.1.7 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-409) exists in MessagePack. Attackers reach the vulnerable code path via Lz4Block without authentication.
Check the vendor advisory for the affected versions of MessagePack. Attack surface: Lz4Block / Lz4BlockArray / MessagePackCompression.Lz4Block / MessagePackCompression.Lz4BlockArray.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 3.1.7.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'MessagePack' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'MessagePack' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
MessagePackを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade MessagePack to 3.1.7ステージング環境で 3.1.7 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com