CVE-2025-66442: In Mbed TLS through 4.0.0, there is a compiler-induced timing side channel (in RSA and CBC/ECB decryption) tha

Q: How do I fix CVE-2025-66442?

mbed tls: upgrade to newer than 4.0.0; tf-psa-crypto: upgrade to newer than 1.0.0. Exact commands for each OS are on this page.

Q: Is CVE-2025-66442 being exploited?

CVE-2025-66442 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-66442 affect?

CVE-2025-66442 affects mbed tls, tf-psa-crypto. Severity is medium (CVSS 5.1). In Mbed TLS through 4.0.0, there is a compiler-induced timing side channel (in RSA and CBC/ECB decryption) that only occurs with LLVM's select-optimize feature. TF-PSA-Crypto through 1.0.0 is also affected.

Q: How urgent is CVE-2025-66442?

Priority 23/100. No elevated risk signals yet.

Routine

MEDIUM 5.1UPGRADEUPGRADE

CVE-2025-66442 is a medium-severity flaw (CVSS 5.1) affecting mbed tls, tf-psa-crypto. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In Mbed TLS through 4.0.0, there is a compiler-induced timing side channel (in RSA and CBC/ECB decryption) that only occurs with LLVM's select-optimize feature. TF-PSA-Crypto through 1.0.0 is also affected.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	5.1 (Medium)
Attack vector	Local
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 81%)
CISA exploited list	No
Weakness	CWE-385
Published	2026-04-01
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: arm

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-01 20:16 UTCPublished CVE record published
2026-06-17 09:56 UTCUpdated Record last modified

arm mbed tls UPGRADE

Affected: <= 4.0.0

Fixed in: newer than 4.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mbed-tls || rpm -q mbed-tls || mbed-tls --version

2. UPGRADE to newer than 4.0.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mbed-tls

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mbed-tls

Note

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

arm tf-psa-crypto UPGRADE

Affected: <= 1.0.0

Fixed in: newer than 1.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy tf-psa-crypto || rpm -q tf-psa-crypto || tf-psa-crypto --version

2. UPGRADE to newer than 1.0.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade tf-psa-crypto

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade tf-psa-crypto

Note

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

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-2025-66442?

mbed tls: upgrade to newer than 4.0.0; tf-psa-crypto: upgrade to newer than 1.0.0. Exact commands for each OS are on this page.

Is CVE-2025-66442 being exploited?

CVE-2025-66442 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-2025-66442 affect?

CVE-2025-66442 affects mbed tls, tf-psa-crypto. Severity is medium (CVSS 5.1). In Mbed TLS through 4.0.0, there is a compiler-induced timing side channel (in RSA and CBC/ECB decryption) that only occurs with LLVM's select-optimize feature. TF-PSA-Crypto through 1.0.0 is also affected.

How urgent is CVE-2025-66442?

Priority 23/100. No elevated risk signals yet.

Related CVEs

CVE-2026-34877 CRITICAL 9.8 UPGRADE DOWNGRADE An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0
CVE-2026-34876 HIGH 7.5 UPGRADE An issue was discovered in Mbed TLS 3.x before 3.6.6
CVE-2026-34875 CRITICAL 9.8 UPGRADE UPGRADE An issue was discovered in Mbed TLS through 3.6.5 and TF-PSA-Crypto 1.0.0
CVE-2026-34874 HIGH 7.5 UPGRADE An issue was discovered in Mbed TLS through 3.6.5 and 4.x through 4.0.0
CVE-2026-34873 CRITICAL 9.1 UPGRADE An issue was discovered in Mbed TLS 3.5.0 through 4.0.0

References

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