# CVE-2026-56786: RTKLIB 2.4.3 - Out-of-bounds Write in decode_type1033 via Crafted RTCM3 Message

> An attacker can achieve arbitrary code execution or denial of service by sending a crafted RTCM3 message to RTKLIB due to an out-of-bounds write.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 25 Jun 2026
- **Updated:** 14 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-56786, GHSA-5cx9-6hw2-hchv, UBUNTU-CVE-2026-56786

## What is CVE-2026-56786?

CVE-2026-56786 is a critical memory corruption vulnerability in tomojitakasu RTKLIB, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

RTKLIB through 2.4.3 contains an out-of-bounds write vulnerability in decode_type1033 function that fails to clamp length counters to destination buffer size, allowing up to 191-byte overflow into fixed 64-byte descriptor fields. An attacker controlling an NTRIP or serial RTCM3 correction stream can craft a valid CRC-bearing type-1033 message to corrupt adjacent rtcm_t object members, potentially achieving arbitrary code execution or denial of service.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-56786?

It affects 1 product.


Products: Rtklib Rtklib.

## How do I fix CVE-2026-56786?

No fix has been published for CVE-2026-56786 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-56786 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56786 exists.

## Other vulnerabilities in tomojitakasu RTKLIB

- [CVE-2026-56789](https://insights.sbomify.com/CVE-2026-56789/): RTKLIB 2.4.3 - Heap Buffer Overflow and Stack Read via Oversized RINEX Epoch Satellite Count (high 7.1)
- [CVE-2026-56787](https://insights.sbomify.com/CVE-2026-56787/): RTKLIB 2.4.3 - Off-by-One Out-of-Bounds Read in decode_ssr3 via RTCM3 SSR Message (medium 6.9)
- [CVE-2026-56788](https://insights.sbomify.com/CVE-2026-56788/): RTKLIB 2.4.3 - Out-of-bounds Read via Negative Array Index in getcodepri (medium 4.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56786 and fix it if it is affected.

What it is: CVE-2026-56786 is a critical memory corruption vulnerability in tomojitakasu RTKLIB, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56786 exists.

Affected product: tomojitakasu RTKLIB. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-56786/ (Markdown: https://insights.sbomify.com/CVE-2026-56786/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56786
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56786
- OSV: https://osv.dev/vulnerability/CVE-2026-56786

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-56786/
Summaries are generated and may contain mistakes; the official description above is the record.