NVD / CVE Program· CNA GitHub_M

CVE-2023-45150: Inviting excessive long email addresses to a calendar event makes the Nextcloud server unresponsive

Noroxi assessment

Priority: Monitor (action score 17/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.47% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
No fixed version is recorded, but the references include a patch (commit or PR) link.

Low priority for now. See the fix and affected versions sections below.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Nextcloud calendar is a calendar app for the Nextcloud server platform. Due to missing precondition checks the server was trying to validate strings of any length as email addresses even when megabytes of data were provided, eventually making the server busy and unresponsive. It is recommended that the Nextcloud Calendar app is upgraded to 4.4.4. The only workaround for users unable to upgrade is to disable the calendar app.

MediumCVSS 4.3 · v3.1—No exploit No fix recorded

Denial of service

BDU:2023-07118

Published: Oct 16, 2023
Updated: Jun 17, 2026
EPSS: 0.4% · 40th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 17 / 40 · 4.3 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.4%

CISA SSVC decision

Exploitation: proof of concept
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 4.3
CNA · GitHub_M: 4.3; agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
nextcloud	calendar	cpe:2.3:a:nextcloud:calendar

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

nextcloud calendar1.0 and later · before 4.4.4

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

nextcloud security-advisories
- >= 1.0.0, < 4.4.4affected

Same product

nextcloud: all records

Other highest-scoring records for the same primary product.

CVE-2022-24838Command Injection in Appointment Emails for Nextcloud Calendar
49Plan
CVE-2025-66511Nextcloud Calendar app used predictable proposal participant tokens
26Monitor
CVE-2023-48308Calendar app returns full stacktrace when an error happens while editing appointment
26Monitor

Published before and after this one in the same product

← EarlierCVE-2018-3763Jul 5, 2018 · In Nextcloud Calendar before 1.5.8 and 1.6.1, a missing sanitization of search results for an autocomplete field could lead to a stored XSS
19Monitor
← EarlierCVE-2023-33183May 30, 2023 · Error in calendar when booking an appointment reveals the full path of the website
17Monitor
Later →CVE-2024-37316Jun 14, 2024 · Nextcloud Calendar's event create can create attachments that link to other websites
18Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

nextcloud/calendarPR 5358

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

NextcloudHackerOne · paid

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: low · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: Low

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

nvd-primary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

github.com/nextcloud/calendar/pull/5358

Show all references (1 more)

github.com/nextcloud/security-advisories/security/advisories/GHSA-r936-8gwm-w452

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records