CVE-2026-58096 in PPP
Summary
by MITRE • 08/26/2026
LcpDecodeConfig() did not validate the length of received endpoint discriminator options against the minimum required by RFC 1717. Undersized options would trigger an out-of-bounds write.
A malicious PPP peer can exploit CVE-2026-58095 and CVE-2026-58096 to crash ppp(8) or potentially execute arbitrary code as root.
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability identified in the LcpDecodeConfig function represents a critical input validation failure within the Point-to-Point Protocol implementation, specifically concerning the handling of endpoint discriminator options. According to RFC 1717, which defines the Link Control Protocol for PPP, there are strict minimum length requirements for configuration options received during link establishment. The software in question fails to verify that incoming option data meets these baseline specifications before processing it further. This oversight creates a scenario where an undersized or malformed endpoint discriminator option can be processed without triggering appropriate bounds checks, leading directly to memory corruption issues such as out-of-bounds writes.
From a technical perspective, the core flaw lies in the absence of rigorous length validation prior to buffer operations. When a malicious PPP peer sends a crafted packet containing an endpoint discriminator option with insufficient data bytes, the decoding routine proceeds under the assumption that valid data is present. Consequently, subsequent memory access patterns exceed the allocated boundaries for internal buffers or structures associated with the configuration parsing logic. This out-of-bounds write can overwrite adjacent memory regions, potentially corrupting critical control flow data such as return addresses on the stack or function pointers in heap-allocated structures. The severity of this flaw is compounded by the fact that PPP operations often run with elevated privileges, meaning successful exploitation grants an attacker significant leverage over the system state.
The operational impact of exploiting CVE-2026-58095 and CVE-2026-58096 is severe, allowing a remote unauthenticated attacker to achieve arbitrary code execution as root or cause a denial of service by crashing the ppp daemon. By carefully crafting the malformed endpoint discriminator option, an adversary can manipulate memory contents to redirect program execution flow. This capability enables the injection and execution of malicious shellcode, effectively compromising the integrity, confidentiality, and availability of the affected system. The ability to crash the process also poses a significant risk for denial-of-service attacks against network infrastructure relying on PPP connections, disrupting service continuity for legitimate users.
This vulnerability aligns with CWE-120, Buffer Copy without Checking Size of Input, as it involves writing data beyond the bounds of a buffer due to insufficient input validation. Furthermore, in the context of the MITRE ATT&CK framework, this flaw facilitates techniques associated with Initial Access and Privilege Escalation, particularly through exploitation of remote services that lack proper authentication or input sanitization mechanisms. The attack vector is classified as network-based, requiring only connectivity to the PPP service rather than local access, which increases its exploitability across diverse environments including dial-up networks, serial links, and certain virtual private network configurations.
Mitigation strategies must focus on implementing strict adherence to RFC 1717 specifications within the LcpDecodeConfig function. Developers should enforce explicit length checks for all received configuration options, ensuring that endpoint discriminator data meets or exceeds the minimum required size before any memory operations are performed. Additionally, incorporating bounds-checking mechanisms during buffer writes can prevent out-of-bounds overwrites even if validation logic is bypassed. Security hardening measures such as running PPP services with reduced privileges where possible and applying timely patches to update the underlying protocol implementation are essential steps to neutralize this threat vector until permanent code fixes are deployed across all affected systems.