Is CVE-2026-25833 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-25833 being exploited in the wild.

How severe is CVE-2026-25833?

High severity, with a CVSS score of 7.5, published 1 April 2026.

Which products and versions are affected?

TrustedFirmware Mbed TLS 3.5.0 to 3.6.5, 4.0.0.

Is there a fix for CVE-2026-25833?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-25833 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-25833?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-25833: Mbed TLS buffer underflow in x509_inet_pton_ipv6

CVE-2026-25833 · Severity: high · CVSS 7.5 · Published 2026-04-01

Mbed TLS, a widely used open-source cryptographic library for embedded devices, contains a flaw in how it processes certain network addresses in digital certificates. An attacker could potentially exploit this to cause a system crash or service outage. This issue primarily affects systems where the library's built-in address parsing is used instead of the operating system's native functions.

Quick answers

Is CVE-2026-25833 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-25833 being exploited in the wild.
How severe is CVE-2026-25833?: High severity, with a CVSS score of 7.5, published 1 April 2026.
Which products and versions are affected?: TrustedFirmware Mbed TLS 3.5.0 to 3.6.5, 4.0.0.
Is there a fix for CVE-2026-25833?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-25833 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-25833?: Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A buffer underflow (specifically a buffer underread) exists in the x509_inet_pton_ipv6() function within Mbed TLS. The vulnerability is triggered when the library uses its internal implementation of inet_pton() (typically when the AF_INET6 macro is undefined by the toolchain). When parsing IPv4-mapped IPv6 addresses, a logic error allows the pointer to walk back up to 4 bytes before the start of the buffer. While primarily a memory underread, this can lead to a Denial of Service (DoS) on platforms with strict memory protection if the read crosses a page boundary. The issue is fixed in versions 3.6.6 and 4.1.0.

Affected products

TrustedFirmware Mbed TLS 3.5.0 to 3.6.5, 4.0.0

Timeline

2026-03-31: advisory: Vendor advisory published
2026-04-01: disclosed: CVE published to NVD

References

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