CVE-2026-48511
CVE-2026-48511 is a high-severity vulnerability in Messagepack with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-407.
Key facts
- Severity: High (CVSS 3.x base score 7.5)
- CVSS v4: 6.3
- EPSS exploit prediction: 0% (14th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-38385
- Weakness: CWE-407
- Affected product: Messagepack
- Published:
- Last modified:
Description
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary<string, object>.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many distinct keys can require repeated linear scans and array copies. For large attacker-controlled maps, this produces quadratic CPU and allocation behavior. The issue is especially surprising because ExpandoObjectResolver.Options is configured with MessagePackSecurity.UntrustedData, but collision-resistant dictionary comparers cannot protect ExpandoObject insertion internals. This vulnerability is fixed in 2.5.301 and 3.1.7.
Frequently asked questions
- What is CVE-2026-48511?
- MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary<string, object>.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many distinct keys can require repeated linear scans and array copies. For large attacker-controlled maps, this produces quadratic CPU and allocation behavior. The issue is especially surprising because ExpandoObjectResolver.Options is configured with MessagePackSecurity.UntrustedData, but collision-resistant dictionary comparers cannot protect ExpandoObject insertion internals. This vulnerability is fixed in 2.5.301 and 3.1.7.
- How severe is CVE-2026-48511?
- CVE-2026-48511 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
- Is CVE-2026-48511 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-48511?
- CVE-2026-48511 affects Messagepack. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-48511?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- Does CVE-2026-48511 have an EU (EUVD) identifier?
- Yes. CVE-2026-48511 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38385.
- When was CVE-2026-48511 published?
- CVE-2026-48511 was published on 2026-06-22 and last updated on 2026-06-25.
References
Affected products (1)
- cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c\#:*:*
More vulnerabilities in Messagepack
- CVE-2026-48509 — Critical (CVSS 9.1): MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, the parameterless…
- CVE-2026-48109 — High (CVSS 8.2): MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, A vulnerability exists in the…
- CVE-2026-48517 — High (CVSS 7.5): MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's typeless…
- CVE-2026-48516 — High (CVSS 7.5): MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7,…
- CVE-2026-48515 — High (CVSS 7.5): MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's…
- CVE-2026-48514 — High (CVSS 7.5): MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7,…
All CVEs affecting Messagepack →
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