CVE-2026-57053: GNU libidn before 1.44 is prone to out-of-bounds reads of uninitialized memory in the ToUnicode APIs because o

Routine

MEDIUM 4.0UPGRADE

CVE-2026-57053 is a medium-severity flaw (CVSS 4.0) affecting libidn. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

GNU libidn before 1.44 is prone to out-of-bounds reads of uninitialized memory in the ToUnicode APIs because of mishandling in idna_to_unicode_internal. The affected code is not present in libidn2.

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	4.0 (Medium)
Attack vector	Local
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.1% (top 97%)
CISA exploited list	No
Weakness	CWE-1284
Published	2026-06-23
Last modified	2026-10-25

Publisher (CNA): MITRE · Vendor: gnu

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-23 18:18 UTCPublished CVE record published
2026-10-25 23:10 UTCUpdated Record last modified

gnu libidn UPGRADE

Affected: >= 0.1.15 and < 1.44

Fixed in: 1.44

Safe to downgrade to: a release before 0.1.15

1. Check installed version

apt-cache policy libidn || rpm -q libidn || libidn --version

2. UPGRADE to 1.44 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade libidn

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libidn

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.1.15 (Debian / Ubuntu)

apt-cache madison libidn sudo apt install libidn=<VERSION_BEFORE_0.1.15> sudo apt-mark hold libidn

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list libidn sudo dnf downgrade libidn-<VERSION_BEFORE_0.1.15> sudo dnf versionlock add libidn

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-57053?

libidn: upgrade to 1.44. Exact commands for each OS are on this page.

Is CVE-2026-57053 being exploited?

CVE-2026-57053 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-57053 affect?

CVE-2026-57053 affects libidn. Severity is medium (CVSS 4.0). GNU libidn before 1.44 is prone to out-of-bounds reads of uninitialized memory in the ToUnicode APIs because of mishandling in idna_to_unicode_internal. The affected code is not present in libidn2.

How urgent is CVE-2026-57053?

Priority 20/100. Public exploit reference

References

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