CVE-2026-114731 Roundcube CVE debrief

Who should care

Defenders responsible for Roundcube Webmail instances should assess exposure and prioritize patching or mitigating this vulnerability to prevent potential denial-of-service attacks.

Why it matters

CVE-2026-114731 is a MEDIUM severity vulnerability affecting Roundcube Webmail. Defenders should prioritize patching or mitigating this vulnerability to prevent potential denial-of-service attacks. The vulnerability allows an attacker to exhaust server memory by referencing an attacker-controlled host. Defenders responsible for Roundcube Webmail instances should assess exposure and take action. The evidence is limited, and further verification is required to determine the full scope of the vulnerability.

• Potential denial-of-service attacks due to uncontrolled resource consumption
• Server memory exhaustion may lead to service unavailability

Technical summary

The vulnerability is caused by an uncontrolled resource consumption issue in the CSS proxy feature of Roundcube Webmail. The fetched stylesheet is read into memory in full, with no size limit and no read timeout, allowing an attacker to exhaust server memory by referencing an attacker-controlled host. This issue can lead to potential denial-of-service attacks and server memory exhaustion. Upstream fixed this in the commit 'Add a size limit to the CSS proxy content processing', which caps the response at 5 MB, reads it as a stream and applies a read timeout.

Defensive priority

Defenders should prioritize patching or mitigating this vulnerability to prevent potential denial-of-service attacks.

Recommended defensive actions

• Apply patches or updates to affected Roundcube Webmail instances
• Restrict access to the CSS proxy feature
• Monitor server memory usage and implement limits
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and source item provide details about the vulnerability, including its description, affected versions, and fixed versions. However, there is no information about exploitation or impact.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.