Perl HTTP::Tiny has insecure TLS default, affecting and other modules

15/04/23 — sgo

UPDATE 2023-06-12: v0.083-TRIAL has been released with a fix.

[CVE-2023-31486] HTTP::Tiny v0.082, is a http client included in Perl (since v5.13.9) and also a standalone CPAN module. It does not verify TLS certificates by default requiring users to opt-in with the verify_SSL=>1 flag to verify the identity of the HTTPS server they are communicating with.

The module is used by many distributions on CPAN, and likely other open source and proprietary software.

NOTE: This post summarizes security problems caused by the insecure default and how it affects code relying on it for https. For a discussion on how this is being addressed upstream, please see RFC: Making SSL_verify safer

Affected CPAN Modules

After PSA: HTTP::Tiny disabled SSL verification by default! was posted on Reddit, we were reminded that this might be a bigger problem than first thought.

So we searched trough metacpan-cpan-extracted to find distributions using HTTP::Tiny without specifying the cert verification behaviour. Distros using it without mentioning verify_SSL somewhere in the code was flagged. See for the full list.

Most distributions we found did not enable the certificate verification feature, potentially exposing users to machine-in-the-middle attacks via a CWE-295: Improper Certificate Validation weakness.

… and more. We have done a search of CPAN and generated a list of 381 potentially problematic distributions.


Upstream for HTTP::Tiny has not provided a patch or mitigation. Suggestions to change the insecure default has been turned down several times over the years due to backwards compatibility concerns.

Upstream for HTTP::Tiny has merged a patch that changes the insecure default from 0 to 1. It is available in the development version HTTP::Tiny v0.083-TRIAL on CPAN, and the change is planned to be included in perl-5.38.0.

An escape hatch environment variable PERL_HTTP_TINY_SSL_INSECURE_BY_DEFAULT=1 has been provided for users who need to restore the previous insecure default after updating.

For additional information, please see the upstream discussion in RFC: Making SSL_verify safer.

To mitigate the risk caused by the CWE-1188: Insecure Default Initialization of Resource weakness, you have some options:

  • Ensure that HTTP::Tiny in your include path is v0.083-TRIAL or newer.

  • Modify affected code using HTTP::Tiny and set verify_SSL=>1.

  • Modify affected code to use a http client with secure defaults, like Mojo::UserAgent or LWP::UserAgent.

  • Patch HTTP::Tiny on your system with a patch that changes the default to verify_SSL=>1.

It’s recommended that users update Mozilla::CA as well, since HTTP::Tiny defaults to trusting certificates provided by that module. Alternatively the environment variable SSL_CERT_FILE can be set to point to the system trust store.


  • 2023-04-18: Add reference to fixed v2.35-TRIAL
  • 2023-04-29: Add CVE identifiers CVE-2023-31484, CVE-2023-31485, CVE-2023-31486
  • 2023-06-12: Add references to fix applied to HTTP::Tiny, GitLab::API::v4, and suggestion to update Mozilla::CA