How severe is CVE-2026-93563?

CVE-2026-93563 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-93563 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (24th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-93563?

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

When was CVE-2026-93563 published?

CVE-2026-93563 was published on 2026-09-18 and last updated on 2026-09-25.

CVE-2026-93563

CVE-2026-93563 is a high-severity vulnerability with a CVSS 3.x base score of 7.5. 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-1035.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 0% (24th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-1035
Published: 2026-09-18
Last modified: 2026-09-25

Description

A flaw was found in Netty's `SmtpResponseDecoder` component. A remote attacker, acting as a malicious or man-in-the-middle (MITM) SMTP server, could exploit this by sending a specially crafted, unbounded multi-line SMTP response without a terminator. This vulnerability leads to unbounded memory accumulation within the client's Java Virtual Machine (JVM) heap, causing an `OutOfMemoryError` and a denial of service (DoS) due to a process crash.

Frequently asked questions

What is CVE-2026-93563?: A flaw was found in Netty's `SmtpResponseDecoder` component. A remote attacker, acting as a malicious or man-in-the-middle (MITM) SMTP server, could exploit this by sending a specially crafted, unbounded multi-line SMTP response without a terminator. This vulnerability leads to unbounded memory accumulation within the client's Java Virtual Machine (JVM) heap, causing an `OutOfMemoryError` and a denial of service (DoS) due to a process crash.
How severe is CVE-2026-93563?: CVE-2026-93563 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-93563 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (24th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-93563?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-93563 published?: CVE-2026-93563 was published on 2026-09-18 and last updated on 2026-09-25.

References

Other CWE-1035 vulnerabilities

CVE-2026-93565 — High (CVSS 7.5): A flaw was found in Netty RtspDecoder. The `RtspMethods.valueOf()` function incorrectly strips trailing control bytes…
CVE-2026-93564 — High (CVSS 7.5): A flaw was found in Netty. A reference-count leak in the HAProxy PROXY-v2 message decoder allows a remote,…
CVE-2026-93558 — High (CVSS 7.5): A flaw was found in Netty's WebSocketServerExtensionHandler. A remote, unauthenticated attacker can exploit this…
CVE-2026-93560 — High (CVSS 7.5): A flaw was found in the Netty STOMP codec. A remote attacker could send a specially crafted STOMP frame with a…
CVE-2026-93575 — High (CVSS 7.5): A flaw was found in Netty's MqttDecoder. An unauthenticated remote attacker can exploit this vulnerability by sending a…
CVE-2026-93494 — High (CVSS 7.5): A flaw was found in Netty's StompSubframeDecoder component. A remote attacker can exploit this vulnerability by sending…

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