Vulnerability in MessagePack (CVE-2026-48502)
Summary
Vulnerability in MessagePack (CVE-2026-48502). Risk of unauthorized operations or information disclosure. Exploitable via tokenSize. Mitigation: upgrade to 3.1.7 or later.
Original description
The description as published by the source.
Summary
MessagePackReader.ReadDateTime() can allocate stack memory based on an attacker-controlled MessagePack extension length. In the slow path for timestamp extension parsing, the computed tokenSize includes the extension body length from the wire and is used in a stackalloc operation before the extension length is validated as one of the valid timestamp sizes.
A very small payload can claim a large timestamp extension body and cause a stack allocation large enough to trigger an uncatchable StackOverflowException, terminating the host process.
Impact
Applications are affected when they deserialize untrusted payloads into types containing DateTime values. This path is available through the standard formatter set and does not require opting into typeless serialization, LZ4 compression, Unity-specific resolvers, or other specialized features.
MessagePackSecurity.UntrustedData and MaximumObjectGraphDepth do not mitigate this issue because the crash is caused by a single-frame stack allocation, not by object graph recursion.
An attacker can send a MessagePack timestamp extension header with an oversized body length and insufficient body bytes. The reader enters the slow path, attempts to stack-allocate a buffer sized from that declared length, and can terminate the process before a catchable serialization exception is thrown.
Affected components
- Package:
MessagePack - API:
MessagePackReader.ReadDateTime - Data types:
DateTimeand formatter…
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-2026-48502 has been found in MessagePack.
Attackers can target a specific entry point like tokenSize 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-2026-48502" on the vendor's site.
CVE-2026-48502 (MessagePack) — CWE-1188 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: tokenSize / stackalloc / StackOverflowException / DateTime
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-1188) exists in MessagePack. Attackers reach the vulnerable code path via tokenSize without authentication.
Check the vendor advisory for the affected versions of MessagePack. Attack surface: tokenSize / stackalloc / StackOverflowException / DateTime.
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