Lenient Parsing of Content-Length Header When Prefixed with Plus Sign

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

3.1 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N

EPSS

• CVE-2021-32715: 1.13% estimated exploitation activity in the next 30 days; percentile 66.34 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary hyper's HTTP/1 server code had a flaw that incorrectly parses and accepts requests with a Content-Length header with a prefixed plus sign, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that doesn't parse such Content-Length headers, but forwards them, can result in "request smuggling" or "desync attacks". Vulnerability The flaw exists in all prior versions of hyper, if built with rustc v1.5.0 or newer. Example: This request gets accepted and hyper reads the body as abc. The request should be rejected, according to RFC 7230, since the ABNF for Content-Length only allows for DIGITs. This is due to using the FromStr implementation for u64 in the standard library. By differing from the spec, it is possible to send requests like these to endpoints that have different HTTP implementations, with different interpretations of the payload semantics, and cause "desync attacks". In this particular case, an upstream proxy would need to error when…

Published by the source

12 Jul 2021, 16:54 UTC

Last modified by the source

3 Apr 2023, 20:26 UTC

Source last checked

26 Oct 2026, 15:33 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-f3pg-qwvg-p99c

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# Patch Next advisory brief: CVE-2021-32715

Advisory: Lenient Parsing of Content-Length Header When Prefixed with Plus Sign
IDs: CVE-2021-32715, GHSA-f3pg-qwvg-p99c
Record: https://patchnext.com/advisories/cve-2021-32715 (revision 1, source checked 26 Oct 2026, 15:33 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: hyper 0.14.10. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io hyper: affected < 0.14.10; fixed in 0.14.10

## Suggested inspection (read-only)
- crates.io hyper: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on hyper.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-f3pg-qwvg-p99c (GitHub-reviewed advisory GHSA-f3pg-qwvg-p99c lists affected ranges: crates.io hyper >=0 <0.14.10)

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