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CVE-2026-5856— Contiki-NG DNS/mDNS Resolver Out-of-Bounds Read via Unchecked skip_name Traversal Before Transaction-ID Validation

Quick assessment

Affected
Contiki-NG Contiki-NG
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Contiki-NG是Contiki-NG组织开源的一个适用于物联网中资源受限设备的操作系统。 Contiki-NG存在缓冲区错误漏洞，该漏洞源于DNS/mDNS解析器中的skip_name()函数在遍历DNS wire格式名称标签时未检查数据包边界，在验证事务ID前根据攻击者控制的nquestions循环调用，可能导致越界读取uip_buf及相邻内存，泄露内存内容或导致解析器崩溃。

CVSS 7.1 · High EPSS 0.25% · P17

Possible ATT&CK Techniques 1 AI

T1560 · Archive Collected Data

Affected Version Matrix 1

VendorProduct Version RangeStatus
Contiki-NG Contiki-NG < 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe affected
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I. Basic Information for CVE-2026-5856

Vulnerability Information
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Vulnerability Title
Contiki-NG DNS/mDNS Resolver Out-of-Bounds Read via Unchecked skip_name Traversal Before Transaction-ID Validation
Source: CVE Program / CVE List V5
Vulnerability Description
Contiki-NG's DNS/mDNS resolver skip_name() in os/services/resolv/resolv.c walks DNS wire-format name labels with no packet-boundary check, and the caller in newdata() invokes it in a loop iterating nquestions times from the attacker-controlled DNS header before validating the transaction ID. An attacker who sets nquestions higher than the number of complete questions present causes skip_name() to walk past the UDP packet buffer, and the returned pointer is cast to struct dns_answer * for further memory reads. On builds with RESOLV_CONF_SUPPORTS_MDNS enabled, any peer on the local segment can trigger the read unauthenticated via a multicast UDP 5353 packet with no outstanding query required; on standard DNS builds an attacker who can inject a UDP response from port 53 during an outstanding query can trigger the same read. Impact is out-of-bounds read of uip_buf and adjacent memory, disclosing memory contents or crashing the resolver.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5
Vulnerability Title
Contiki-NG 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Contiki-NG是Contiki-NG组织开源的一个适用于物联网中资源受限设备的操作系统。 Contiki-NG存在缓冲区错误漏洞，该漏洞源于DNS/mDNS解析器中的skip_name()函数在遍历DNS wire格式名称标签时未检查数据包边界，在验证事务ID前根据攻击者控制的nquestions循环调用，可能导致越界读取uip_buf及相邻内存，泄露内存内容或导致解析器崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Contiki-NG Contiki-NG 0 ~ 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe -

II. Public POCs for CVE-2026-5856

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8022 chars
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III. Intelligence Information for CVE-2026-5856

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Patches & Fixes for CVE-2026-5856 (2)

Vendor Pages for CVE-2026-5856 (1)

Same Patch Batch · Contiki-NG · 2026-08-06 · 3 CVEs total

CVE-2026-5857 8.1 HIGH Contiki-NG MQTT Client Out-of-Bounds Write in PUBLISH Topic Parser via Persistent State Be
CVE-2026-5855 7.5 HIGH Contiki-NG LwM2M TLV Parser Out-of-Bounds Read via Unchecked Buffer Length in lwm2m_tlv_re

IV. Related Vulnerabilities

Same product: Contiki-NG
Same vendor: Contiki-NG
Same weakness: CWE-125

V. Comments for CVE-2026-5856

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