# CVE-2026-56787: RTKLIB off-by-one error in decode_ssr3 function

Source: https://junglewise.ai/threats/cve-2026-56787-rtklib-off-by-one-error-in-decode-ssr3-function  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-25. Updated: 2026-06-25  
License: CC BY 4.0 with a link back

CVE-2026-56787 · Severity: medium · CVSS 6.5 · Published 2026-06-25

RTKLIB is an open-source library used for high-precision satellite positioning in GPS/GNSS receivers and base stations. A vulnerability in how the software processes correction data allows a remote attacker to send a specially crafted message that can crash the system. This could lead to a loss of positioning services for mobile rovers or the failure of permanent reference stations (CORS) used in surveying and navigation.

Technologies: [Tomoji Takasu RTKLIB](https://junglewise.ai/threats/technologies/rtklib). Vendors: [Tomoji Takasu](https://junglewise.ai/threats/vendors/tomoji-takasu).

## Quick answers

**Is CVE-2026-56787 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56787 being exploited in the wild.

**How severe is CVE-2026-56787?** Medium severity, with a CVSS score of 6.5, published 25 June 2026.

**Which products and versions are affected?** Tomoji Takasu RTKLIB through 2.4.3.

**Is there a fix for CVE-2026-56787?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-56787 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-56787?** Check whether you run Tomoji Takasu RTKLIB at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An off-by-one error exists in the `decode_ssr3` function within `src/rtcm3.c` at line 1446. The vulnerability is triggered when processing RTCM3 State Space Representation (SSR) messages containing attacker-controlled signal mode fields. By sending a crafted SSR correction stream via NTRIP or serial connections, a remote attacker can cause an out-of-bounds read leading to a global buffer overflow. This results in a denial-of-service (DoS) condition, crashing RTKLIB-based rovers or CORS servers. As of the advisory date, the issue affects all versions through 2.4.3.

## Affected products

- tomojitakasu RTKLIB through 2.4.3

## Timeline

- 2026-06-09: disclosed: Issue reported on GitHub by researcher raefko (FuzzingLabs)
- 2026-06-25: advisory: NVD and VulnCheck published advisory details

## References

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

## Related threats

- [RTKLIB heap buffer overflow in readrnxobsb function](https://junglewise.ai/threats/cve-2026-56789-rtklib-heap-buffer-overflow-in-readrnxobsb-function)
- [RTKLIB out-of-bounds read in getcodepri function](https://junglewise.ai/threats/cve-2026-56788-rtklib-out-of-bounds-read-in-getcodepri-function)
- [RTKLIB out-of-bounds write in decode_type1033](https://junglewise.ai/threats/cve-2026-56786-rtklib-out-of-bounds-write-in-decode-type1033)