CVE-2026-18220 in Red Hat
Summary
by MITRE • 07/29/2026
An out-of-bounds write vulnerability was found in the BFD library's DLX ELF backend (bfd/elf32-dlx.c) in GNU binutils. The dlx_rtype_to_howto() function maps ELF relocation types to internal howto structures but fails to perform adequate bounds checking on attacker-controlled relocation type values (via ELF32_R_TYPE(r_info)) before indexing into the dlx_elf_howto_table[] array. The DLX relocation type number space is non-contiguous (basic types 0-6, extended types at 0x10000+), but the default case in the switch statement allows arbitrary index values to reach the array access.
A specially crafted ELF/DLX object file can trigger this out-of-bounds write when processed by any BFD-consuming tool (objdump, readelf, strip, ld, nm, objcopy). The vulnerability has been demonstrated to achieve arbitrary code execution via a File Stream Oriented Programming (FSOP) attack against glibc FILE structures (stderr), redirecting control flow to system().
Attack scenarios include CI/CD pipelines performing automated binary analysis, developer workstations running objdump/readelf on untrusted binaries, automated security scanning or malware analysis tools invoking binutils, and package build systems processing third-party code.
Note: This vulnerability is only exploitable when binutils is built with the DLX backend enabled (typically via --enable-targets=all).
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Analysis
by VulDB Data Team • 07/29/2026
The vulnerability under examination represents a critical out-of-bounds write flaw within the GNU binutils BFD library's DLX ELF backend implementation. This issue resides in the bfd/elf32-dlx.c file where the dlx_rtype_to_howto() function processes ELF relocation information without proper validation of input parameters. The fundamental problem occurs when the function extracts relocation type values from ELF32_R_TYPE(r_info) and directly uses these values as array indices into the dlx_elf_howto_table[] structure. This lack of bounds checking creates a predictable path for attackers to manipulate memory access patterns through carefully crafted ELF files targeting the DLX architecture.
The technical implementation of this vulnerability stems from the non-contiguous nature of DLX relocation type numbering where basic types range from 0-6 while extended types begin at 0x10000 and beyond. The switch statement within dlx_rtype_to_howto() lacks proper handling for values outside the expected range, allowing any arbitrary integer value to fall through to the default case. When this occurs, the function performs direct array indexing using the attacker-controlled relocation type value, which can result in writing data beyond the allocated bounds of the dlx_elf_howto_table[] array. This flaw manifests across all BFD-consuming tools including objdump, readelf, strip, ld, nm, and objcopy, making it particularly dangerous given the widespread use of these utilities in development and security workflows.
The operational impact of this vulnerability extends beyond simple memory corruption, as demonstrated through successful exploitation techniques that leverage File Stream Oriented Programming attacks against glibc FILE structures. Specifically, attackers can redirect control flow to system() by manipulating stderr structures through the out-of-bounds write primitive, achieving arbitrary code execution capabilities. This exploit path aligns with common attack patterns documented in the MITRE ATT&CK framework under technique T1059 for command and script injection, while also mapping to CWE-787 which specifically addresses out-of-bounds writes. The vulnerability's exploitation potential is particularly concerning in automated environments such as CI/CD pipelines where binaries are processed without user intervention, or in security scanning tools that automatically analyze potentially malicious files.
The attack vectors for this vulnerability encompass multiple operational domains including developer workstations where objdump and readelf are routinely executed on untrusted binaries, automated malware analysis systems that invoke binutils utilities, and package build environments that process third-party code. The exploitation requires only that binutils be compiled with DLX backend support typically enabled via --enable-targets=all configuration option, making it potentially accessible in various deployment scenarios. Security professionals should consider this vulnerability when implementing defense-in-depth strategies as it represents a path to privilege escalation or arbitrary code execution through legitimate system utilities. Organizations should prioritize patching affected systems and implementing runtime protections such as address space layout randomization and stack canaries while also considering input validation controls at the toolchain level to prevent exploitation through untrusted binary processing workflows.