Infinite loop in Nut/OS TCP options parser enables denial of service
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- No fix listed
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA. Impact type from CWE-835.
Summary
Nut/OS releases up to version 5.1 include the Nut/Net TCP/IP stack developed by Ethernut/Egnite. A flaw in the TCP options parser (CWE-835) causes an infinite loop in the function NutTcpInputOptions when a malformed TCP option is processed. An unauthenticated remote attacker can send a single TCP segment to any open TCP port, which blocks TCP processing and makes all TCP-based services unresponsive until the device is rebooted.
Written with Claude Haiku 5.5 from the sources below · 2026-11-05
Description from the CNA
A remotely exploitable denial-of-service vulnerability exists in the TCP options parser of the Nut/Net TCP/IP stack included in Nut/OS, developed by Ethernut/Egnite. Nut/OS releases up to version 5.1 are affected. An unauthenticated attacker can send a single TCP segment containing an unknown TCP option with a length byte of zero to any open TCP port on a vulnerable device. When processed, this malformed option triggers an infinite loop in the function NutTcpInputOptions, permanently blocking the TCP processing thread and rendering all TCP-based services unresponsive until the device is rebooted.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Ethernut / egnite GmbH | Nut/Net TCP/IP Stack | Nut/OS 5.1 | — | No fix listed | CNA |
- Nut/Net TCP/IP Stack VendorEthernut / egnite GmbH Affected Nut/OS 5.1 Fixed in — No fix listed CNA
Remediation
The sources list no fixed version for Nut/Net TCP/IP Stack.
Written with Claude Haiku 5.5 from the sources below · 2026-11-05
Timeline
- 2026-11-02 Threatist record created from CVE-2026-120596
- 2026-11-02 CVSS score added · CISA ADP
- 2026-11-02 Weakness changed · CISA ADP
- 2026-11-02 CISA SSVC decision points changed
- 2026-11-02 Alias added: GHSA-mg75-66wv-hfxw
References
Sources
- CVE-2026-120596 · CVE Program
- CVE-2026-120596 · NVD
- FIRST EPSS
- GHSA-mg75-66wv-hfxw · GitHub Advisory Database · CC BY 4.0
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