VulnerabilityPublished 11 Mar 2026Updated 12 Mar 2026

CVE-2026-27703: RIOT · Out-of-bounds Write

Affects RIOTSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.5% chance of exploitation in 30 days – higher than 42% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
RIOT-OSRIOT	Affected <=2026.01	Fixed in–
GitHubriot-os/RIOT`pkg:github/riot-os/RIOT`Other threats	Affected <=2026.01	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2026-27703, organizations should prioritize upgrading to a patched version of RIOT-OS once available. In the interim, implement strict input validation on CoAP requests, particularly on option data sizes, to prevent buffer overflows. Employ runtime protections such as stack canaries and address space layout randomization (ASLR) where supported by the hardware and OS configuration. Network segmentation and firewall rules should restrict access to CoAP services to trusted sources only, minimizing exposure to untrusted networks. Conduct thorough code audits and fuzz testing on CoAP handlers to identify and remediate similar memory safety issues. Additionally, monitor device behavior for anomalies indicative of exploitation attempts, such as unexpected crashes or unusual network traffic. Collaborate with RIOT-OS maintainers and the IoT security community to stay informed on patch releases and emerging threats. For critical deployments, consider deploying intrusion detection systems capable of recognizing exploitation patterns targeting this vulnerability.

Description

CVE-2026-27703 is a high-severity out-of-bounds write vulnerability in RIOT-OS, an open-source operating system for IoT and embedded devices. The flaw exists in the default handler for the coap_well_known_core resource, which writes user-supplied option data into a fixed-size buffer without proper size validation. This can lead to corruption of adjacent stack memory, including critical control flow data such as return addresses. Exploitation can result in denial of service or arbitrary code execution without requiring authentication or user interaction. The vulnerability affects RIOT versions up to and including 2026.01. Although no known exploits are currently reported in the wild, the ease of remote exploitation and potential impact on device integrity make this a significant threat. Organizations deploying RIOT-OS in IoT environments should prioritize patching and implement strict input validation and memory safety practices to mitigate risk.

Impact

The vulnerability poses a significant risk to organizations deploying RIOT-OS in IoT and embedded environments. Exploitation can lead to arbitrary code execution, allowing attackers to take control of affected devices, potentially pivoting into larger networks or disrupting critical IoT functions. This can result in denial of service conditions, loss of device integrity, and compromise of sensitive operations managed by these devices. Given the widespread adoption of RIOT-OS in various sectors including industrial control, smart cities, healthcare devices, and consumer IoT, the impact can extend to critical infrastructure and safety systems. The remote and unauthenticated nature of the exploit increases the attack surface, enabling attackers to target devices at scale. Organizations may face operational disruptions, data integrity breaches, and increased risk of lateral movement within networks. The absence of known exploits currently provides a window for proactive mitigation, but also indicates potential for future exploitation as attackers develop weaponized payloads.

Summary

CVE-2026-27703 is an out-of-bounds write vulnerability classified under CWE-787, affecting the RIOT-OS operating system versions 2026.01 and earlier. RIOT-OS is widely used in IoT and embedded devices due to its lightweight design tailored for constrained hardware. The vulnerability resides in the coap_well_known_core_default_handler function, which handles requests to the well-known core resource in the CoAP protocol. This handler writes user-provided option data and other response data into a fixed-size buffer without verifying that the buffer can accommodate the entire response. Consequently, an attacker can supply crafted input that causes the handler to write beyond the buffer boundary, corrupting adjacent stack memory. This corruption can overwrite security-critical data such as return addresses, enabling control flow hijacking. The vulnerability is remotely exploitable over the network without any authentication or user interaction, increasing its risk profile. While no public exploits have been observed, the vulnerability’s characteristics suggest potential for denial of service or arbitrary code execution attacks on vulnerable IoT devices. The CVSS v3.1 score of 7.5 reflects its high severity, driven by network attack vector, low attack complexity, and impact on integrity without affecting confidentiality or availability. The lack of available patches at the time of disclosure underscores the need for immediate attention from RIOT-OS users and maintainers.

CWE-787Out-of-bounds Write (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #5
The product writes data past the end, or before the beginning, of the intended buffer.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/RIOT-OS/RIOT/security/advisories/GHSA-qgj4-9jff-93cj (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 19 Mar 2026, 02:16 UTC

WeaknessesCWE-787

Technical details

References

Community reviews

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