CVE-2024-50383 in Botan
Summary
by MITRE • 10/23/2024
Botan before 3.6.0, when certain GCC versions are used, has a compiler-induced secret-dependent operation in lib/utils/donna128.h in donna128 (used in Chacha-Poly1305 and x25519). An addition can be skipped if a carry is not set. This was observed for GCC 11.3.0 with -O2 on MIPS, and GCC on x86-i386. (Only 32-bit processors can be affected.)
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Analysis
by VulDB Data Team • 10/31/2024
This vulnerability resides in the Botan cryptographic library version 3.6.0 and earlier, specifically affecting implementations that utilize certain GCC compiler versions with particular optimization levels. The flaw manifests in the donna128 library component which handles 128-bit arithmetic operations crucial for cryptographic functions including ChaCha-Poly1305 and x25519. The vulnerability stems from compiler optimizations that can cause conditional operations to be skipped when carry flags are not properly set during arithmetic computations. This behavior creates a timing-dependent execution path that could potentially leak information about secret values through side-channel analysis.
The technical implementation issue occurs within the donna128.h file where arithmetic operations are implemented using compiler-generated code that assumes certain carry propagation behaviors. When GCC 11.3.0 compiles code with -O2 optimization level on MIPS and x86-i386 architectures, the compiler may optimize away conditional addition operations that should execute based on carry flags. This optimization becomes problematic because cryptographic algorithms require constant-time execution to prevent attackers from inferring secret information through timing variations. The vulnerability specifically affects 32-bit processors where the compiler's optimization strategies interact more aggressively with the underlying hardware's carry propagation mechanisms.
The operational impact of this vulnerability is significant for systems relying on Botan's cryptographic implementations, particularly those using ChaCha-Poly1305 for authenticated encryption or x25519 for key exchange. Attackers could potentially exploit this timing variation to perform side-channel attacks that infer information about private keys or other cryptographic secrets. The vulnerability creates a potential attack surface for sophisticated adversaries who can monitor execution timing patterns and correlate them with secret-dependent operations. This type of vulnerability falls under the category of timing side channels and aligns with CWE-203, which addresses exposure of sensitive information through side channels.
The vulnerability demonstrates a critical gap in compiler optimization assumptions within cryptographic software implementation. It highlights how modern compiler optimizations designed for performance can inadvertently create security weaknesses when applied to cryptographic code that requires constant-time execution characteristics. This issue particularly affects systems where cryptographic operations are performed on embedded or specialized hardware where timing variations can be more easily monitored and analyzed. The attack vector aligns with ATT&CK technique T1059.001 for command and scripting interpreter and T1566.001 for spearphishing attachment, as attackers could potentially use this weakness to compromise systems through targeted attacks on cryptographic implementations.
Mitigation strategies include upgrading to Botan version 3.6.0 or later where the issue has been addressed through code modifications that ensure consistent execution paths regardless of compiler optimizations. System administrators should also consider disabling specific compiler optimizations for cryptographic code sections or using alternative compiler versions that do not exhibit this behavior. Additionally, implementing proper constant-time implementation practices in cryptographic code can help prevent similar issues from occurring in the future. Organizations should review their cryptographic implementations to ensure they are not susceptible to similar compiler-induced timing variations, particularly when using aggressive optimization levels with specific compiler versions on targeted architectures.