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DHCP server unbounded option parsing - OOB read from packet buffer

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@cms19859230182-lang 已經在處理了。

開始於 2026年10月8日。

  • #11858 來自 @cms19859230182-lang —— 未關閉

評估

難度
3/5
預估耗時
1-2 天
新手友好度
68/100
Issue 類型
缺陷
描述清晰度
描述清楚
活躍度
冷清
技術堆疊
c
領域
embedded-iot, networking, security

研究方向

從 components/net/lwip-dhcpd/dhcp_server.c 的第 346 行開始，追蹤接收封包的長度和選項位置是如何表示的。使用 AddressSanitizer 建置 DHCP 伺服器，並傳送所描述的格式錯誤 DHCP 封包，其中包括缺少的結束標記和過大的選項長度。當格式錯誤的選項不再導致讀取超出封包緩衝區時，即表示完成。

由索引模型根據 Issue 內容生成。

描述

RT-Thread Version

tested HEAD, commit 38c007af

Hardware Type/Architectures

independent (Bug is in lwip-dhcpd C implementation)

Develop Toolchain

Other

Describe the bug
Summary

A buffer over-read vulnerability exists in RT-Thread's DHCP server implementation (components/net/lwip-dhcpd/dhcp_server.c) where the DHCP option parsing loop has no bounds check on the input buffer position, allowing a crafted DHCP packet to read past the allocated buffer.

Details

File: components/net/lwip-dhcpd/dhcp_server.c, line 346

The DHCP options parsing loop uses while(finished == 0) to iterate through options in the received packet. The loop reads option type and length fields from the packet data but does NOT check whether the current read position exceeds the packet buffer boundary.

/* dhcp_server.c:346 */
while(finished == 0) {
    /* reads option type and length from packet data */
    /* NO check that position < packet_length */
}

Since DHCP packets are received over the network with no authentication, this is reachable pre-authentication on the local network segment.

PoC

Send a crafted DHCP packet on the local network segment with:

  • Valid DHCP header (op=1, htype=1, hlen=6)
  • Options section containing a chain of options where each option's length field points past the end of the packet
  • No DHCP_OPTION_END (0xFF) marker

The server's option parsing loop will read past the packet buffer boundary until it hits unmapped memory (crash) or reads adjacent heap data (info leak).

Build and run the RT-Thread DHCP server component with AddressSanitizer enabled to observe the over-read:

# Cross-compile RT-Thread with ASAN, enable lwip-dhcpd,
# send crafted DHCP DISCOVER on the local interface
Other additional context
Impact
  • Out-of-bounds read from the packet buffer
  • Potential information disclosure from adjacent heap memory
  • Potential crash (DoS) if reading into unmapped memory
  • Affects any RT-Thread device running the built-in DHCP server
  • Attack vector: adjacent network (DHCP is link-local), no authentication required

Suggested fix:

- while(finished == 0) {
+ while(finished == 0 && position < packet_length) {

Also validate that position + option_length does not exceed packet_length before reading option data.

主要語言
C
星號
12.3k
分支
5.5k
平均合併
6 天 32 分鐘
30 天內合併 PR
24

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