Summary
IP Restriction Middleware in Hono is vulnerable to an IP address validation bypass. The IPV4_REGEX pattern and convertIPv4ToBinary function in src/utils/ipaddr.ts do not properly validate that IPv4 octet values are within the valid range of 0-255, allowing attackers to craft malformed IP addresses that bypass IP-based access controls.
Details
The vulnerability exists in two components:
- Permissive regex pattern: The
IPV4_REGEX (/^[0-9]{0,3}\.[0-9]{0,3}\.[0-9]{0,3}\.[0-9]{0,3}$/) accepts octet values greater than 255 (e.g., 999).
- Unsafe binary conversion: The
convertIPv4ToBinary function does not validate octet ranges before performing bitwise operations. When an octet exceeds 255, it overflows into adjacent octets during the bit-shift calculation.
For example, the IP address 1.2.2.355 is accepted and converts to the same binary value as 1.2.3.99:
355 = 256 + 99 = 0x163- After bit-shifting:
(1 << 24) + (2 << 16) + (2 << 8) + 355 = 0x01020363 = 1.2.3.99
Impact
An attacker can bypass IP-based restrictions by crafting malformed IP addresses:
- Blocklist bypass: If
1.2.3.0/24 is blocked, an attacker can use 1.2.2.355 (or similar) to bypass the restriction.
- Allowlist bypass: Requests from unauthorized IP ranges may be incorrectly permitted.
This is exploitable when the application relies on client-provided IP addresses (e.g., X-Forwarded-For header) for access control decisions.
Affected Components
- IP Restriction Middleware
src/utils/ipaddr.ts: IPV4_REGEX, convertIPv4ToBinary, distinctRemoteAddr
References
devanshbatham Reporter
Summary
IP Restriction Middleware in Hono is vulnerable to an IP address validation bypass. The
IPV4_REGEXpattern andconvertIPv4ToBinaryfunction insrc/utils/ipaddr.tsdo not properly validate that IPv4 octet values are within the valid range of 0-255, allowing attackers to craft malformed IP addresses that bypass IP-based access controls.Details
The vulnerability exists in two components:
IPV4_REGEX (/^[0-9]{0,3}\.[0-9]{0,3}\.[0-9]{0,3}\.[0-9]{0,3}$/)accepts octet values greater than 255 (e.g.,999).convertIPv4ToBinaryfunction does not validate octet ranges before performing bitwise operations. When an octet exceeds 255, it overflows into adjacent octets during the bit-shift calculation.For example, the IP address
1.2.2.355is accepted and converts to the same binary value as 1.2.3.99:355=256 + 99=0x163(1 << 24) + (2 << 16) + (2 << 8) + 355=0x01020363=1.2.3.99Impact
An attacker can bypass IP-based restrictions by crafting malformed IP addresses:
1.2.3.0/24is blocked, an attacker can use1.2.2.355(or similar) to bypass the restriction.This is exploitable when the application relies on client-provided IP addresses (e.g.,
X-Forwarded-For header) for access control decisions.Affected Components
src/utils/ipaddr.ts:IPV4_REGEX,convertIPv4ToBinary,distinctRemoteAddrReferences