{"id":"CVE-2026-44375","aliases":["GHSA-2cwq-pwfr-wcw3"],"url":"https://o3.security/vulnerability/CVE-2026-44375","summary":"Nerdbank.MessagePack: Attacker-controlled stackalloc in DateTime decoding causes process-terminating StackOverflowException","details":"### Summary\n\nNerdbank.MessagePack contains an uncontrolled stack allocation vulnerability in DateTime decoding. A malicious MessagePack payload can declare an oversized timestamp extension length, causing the reader to allocate an attacker-controlled number of bytes on the stack. This can trigger a `StackOverflowException`, which is not catchable by user code and terminates the process.\n\n### Impact\n\nApplications are impacted if they deserialize MessagePack data from untrusted or attacker-controlled sources using Nerdbank.MessagePack and the target type contains a `DateTime` value.\n\nA small malicious payload can cause process termination, resulting in a denial of service. This may affect services, APIs, workers, message consumers, or other long-running processes that deserialize untrusted MessagePack input.\n\nThe issue occurs because DateTime timestamp extension decoding derives `tokenSize` from the attacker-controlled extension length before validating that the timestamp length is one of the legal MessagePack timestamp sizes: 4, 8, or 12 bytes. When the buffer is incomplete, that unvalidated size is propagated to the streaming reader slow path, where it is used in a `stackalloc`.\n\n### Patches\n\nThe 1.1.62 version contains the fix for this security vulnerability.\n\n### Workarounds\n\nIf upgrading is not yet possible, avoid deserializing untrusted MessagePack payloads into type graphs that may contain `DateTime` fields or properties.\n\nInput byte-size limits alone may not fully mitigate this issue, because the malicious payload can be small while declaring a very large extension length. Possible mitigations include:\n\n- Pre-validating MessagePack extension headers before deserialization and rejecting timestamp extensions whose length is not 4, 8, or 12 bytes.\n- Rejecting or filtering extension type `-1` timestamp values from untrusted input unless they are known to be valid.\n- Running deserialization of untrusted payloads in an isolated process that can be safely restarted after termination.\n- Restricting MessagePack deserialization to trusted producers until a patched version is available.\n\n### Resources\n\n- CWE-789: Uncontrolled Memory Allocation: https://cwe.mitre.org/data/definitions/789.html\n- MessagePack timestamp extension specification: https://github.com/msgpack/msgpack/blob/master/spec.md#timestamp-extension-type","published":"2026-05-14T14:32:09.506Z","modified":"2026-08-12T03:51:37.987488196Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00353,"percentile":0.28871,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"NuGet","name":"Nerdbank.MessagePack","fixedVersion":"1.1.62"}],"fix":{"url":"https://github.com/AArnott/Nerdbank.MessagePack/commit/7d1eb319cfabe7280e70699946c9a48579fa2f30","label":"AArnott/Nerdbank.MessagePack@7d1eb31"},"references":[{"type":"WEB","url":"https://github.com/AArnott/Nerdbank.MessagePack/releases/tag/v1.1.62"},{"type":"ADVISORY","url":"https://github.com/AArnott/Nerdbank.MessagePack/security/advisories/GHSA-2cwq-pwfr-wcw3"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44375.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44375"},{"type":"FIX","url":"https://github.com/AArnott/Nerdbank.MessagePack/commit/7d1eb319cfabe7280e70699946c9a48579fa2f30"},{"type":"FIX","url":"https://github.com/AArnott/Nerdbank.MessagePack/pull/941"},{"type":"PACKAGE","url":"https://github.com/AArnott/Nerdbank.MessagePack"},{"type":"WEB","url":"https://github.com/msgpack/msgpack/blob/master/spec.md#timestamp-extension-type"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:37.987488196Z"}}