Is CVE-2021-21257 actively exploited?

No active exploitation of CVE-2021-21257 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-21257 be exploited remotely?

Yes. CVE-2021-21257 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-21257?

CVE-2021-21257 has a CVSS score of 7.5 (HIGH).

HOME VULNERABILITIESCVE-2021-21257

HIGH

CVE-2021-21257

CWE-787Published: June 18, 2021· Updated: Jun 17, 2026

7.5

CVSS v3.1

Official Description

Contiki-NG is an open-source, cross-platform operating system for internet of things devices. The RPL-Classic and RPL-Lite implementations in the Contiki-NG operating system versions prior to 4.6 do not validate the address pointer in the RPL source routing header This makes it possible for an attacker to cause out-of-bounds writes with packets injected into the network stack. Specifically, the problem lies in the rpl_ext_header_srh_update function in the two rpl-ext-header.c modules for RPL-Classic and RPL-Lite respectively. The addr_ptr variable is calculated using an unvalidated CMPR field value from the source routing header. An out-of-bounds write can be triggered on line 151 in os/net/routing/rpl-lite/rpl-ext-header.c and line 261 in os/net/routing/rpl-classic/rpl-ext-header.c, which contain the following memcpy call with addr_ptr as destination. The problem has been patched in Contiki-NG 4.6. Users can apply a patch out-of-band as a workaround.

NVD Source

Technical Analysis

CVE-2021-21257 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

From a weakness classification perspective (CWE-787): Out-of-bounds write vulnerabilities can lead to data corruption, crashes, or arbitrary code execution.