---
id: "GO-2026-6905"
page: "https://infrastack.ai/live/GO-2026-6905"
kind: "vulnerability"
aliases: ["GO-2026-6905"]
title: "Panic on negative member size in Reader.Read in github.com/blakesmith/ar"
severity: "low"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "github.com/blakesmith/ar", "fixed": [], "affected": "all versions", "ecosystem": "go"}]
ecosystems: ["go"]
tags: ["ar-archives", "deb-parsing", "go", "package"]
not_affected_if: ["no-ar-parsing", "trusted-input-only"]
published_at: "2026-11-05T22:55:15+00:00"
first_seen_at: "2026-11-06T00:09:14+00:00"
updated_at: "2026-11-06T00:10:30+00:00"
sources: [{"source": "govuln", "url": "https://pkg.go.dev/vuln/GO-2026-6905", "first_seen_at": "2026-11-06T00:09:14+00:00"}]
exploit_sources: []
---

# Panic on negative member size in Reader.Read in github.com/blakesmith/ar

Link for people: https://infrastack.ai/live/GO-2026-6905 (this .md is for agents)

The github.com/blakesmith/ar Go package accepts a negative member size in an archive header. Reading that member makes the program panic with a slice bounds error, which crashes any code that parses untrusted ar archives.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- go:github.com/blakesmith/ar affected all versions fixed no fixed version listed

## How to check

- Check whether the project depends on `github.com/blakesmith/ar` with `go list -m github.com/blakesmith/ar`
- Confirm the version in use against the fixed version listed in the advisory (unknown in the sources)

## Timeline

- 2026-11-06T00:09:14+00:00 govuln https://pkg.go.dev/vuln/GO-2026-6905

## From the sources

Reader.Next parses the 10-byte decimal size field of an archive member header with strconv.ParseInt without rejecting negative values. A header with a negative size leaves the reader with a negative remaining byte count, causing the subsequent call to Reader.Read to panic with a slice bounds out of range error when slicing the caller's buffer.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_