How severe is CVE-2026-34877?

CVE-2026-34877 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-34877 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (34th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-34877?

CVE-2026-34877 primarily affects Arm Mbed Tls. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-34877?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-34877 have an EU (EUVD) identifier?

Yes. CVE-2026-34877 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18394.

When was CVE-2026-34877 published?

CVE-2026-34877 was published on 2026-04-02 and last updated on 2026-06-17.

CVE-2026-34877

CVE-2026-34877 is a critical-severity vulnerability in Arm Mbed Tls with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-250.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 0% (34th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-18394
Weakness: CWE-250
Affected product: Arm Mbed Tls
Published: 2026-04-02
Last modified: 2026-06-17

Description

An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.

Frequently asked questions

What is CVE-2026-34877?: An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.
How severe is CVE-2026-34877?: CVE-2026-34877 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-34877 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (34th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-34877?: CVE-2026-34877 primarily affects Arm Mbed Tls. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-34877?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-34877 have an EU (EUVD) identifier?: Yes. CVE-2026-34877 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18394.
When was CVE-2026-34877 published?: CVE-2026-34877 was published on 2026-04-02 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:arm:mbed_tls:*:*:*:*:*:*:*:*
cpe:2.3:a:trustedfirmware:mbed_tls:4.0.0:*:*:*:*:*:*:*

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