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

> Out-of-bounds write in binutils DLX backend allows arbitrary code execution when processing crafted ELF files, requiring the DLX backend to be enabled.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 29 Jul 2026
- **Updated:** 29 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-18220, GHSA-9x84-fgv4-3chj

## What is CVE-2026-18220?

CVE-2026-18220 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 29 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official 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).

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-18220?


## How do I fix CVE-2026-18220?

Apply the vendor's patch.

## Is CVE-2026-18220 being exploited?

There is no known exploitation of CVE-2026-18220 in the wild and no public exploit code.

Public exploit code:

- Proof of Concept (PoC) demonstrating the CVE-2026-18220, an out-of-bounds (OOB) write vulnerability in the DLX ELF backend of GNU binutils (specifically triggered via `objdump -g`) (github_poc): https://github.com/4D4J/objdump-Out-Of-Bounds-write

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18220 and fix it if it is affected.

What it is: CVE-2026-18220 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 29 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-18220 in the wild and no public exploit code.

Affected product: Red Hat Enterprise Linux 10. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18220/ (Markdown: https://insights.sbomify.com/CVE-2026-18220/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18220
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18220
- OSV: https://osv.dev/vulnerability/CVE-2026-18220

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-18220/
Summaries are generated and may contain mistakes; the official description above is the record.