CVE-2026-33635 | iCalendar up to 2.12.1 Icalendar::Values crlf injection (GHSA-pv9c-9mfh-hvxq)

VDB-353755 · CVE-2026-33635 · GHSA-PV9C-9MFH-HVXQ ICALENDAR UP TO 2.12.1 ICALENDAR::VALUES CRLF INJECTION HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 4.2 $0-$5k 1.10+ Summaryinfo A vulnerability has been found in iCalendar up to 2.12.1 and classified as problematic. The affected element is the function Icalendar::Values. This manipulation causes crlf injection. This vulnerability is registered as CVE-2026-33635. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded. Detailsinfo A vulnerability classified as problematic was found in iCalendar up to 2.12.1. Affected by this vulnerability is the function Icalendar::Values. The manipulation with an unknown input leads to a crlf injection vulnerability. The CWE definition for the vulnerability is CWE-93. The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs. As an impact it is known to affect integrity. The summary by CVE is: iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\r` or `\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue. It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-33635 since 03/23/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. Upgrading to version 2.12.2 eliminates this vulnerability. Applying the patch b8d23b490363ee5fffaec1d269a8618a912ca265 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version. Productinfo Type Calendar Software Name iCalendar Version 2.12.0 2.12.1 License open-source Website Product: https://github.com/icalendar/icalendar/ CPE 2.3info 🔒 🔒 CPE 2.2info 🔒 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 4.3 VulDB Meta Temp Score: 4.2 VulDB Base Score: 4.3 VulDB Temp Score: 4.1 VulDB Vector: 🔒 VulDB Reliability: 🔍 CNA Base Score: 4.3 CNA Vector (GitHub_M): 🔒 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Crlf injection CWE: CWE-93 / CWE-74 / CWE-707 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Yes Availability: 🔒 Status: Not defined Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock Threat Intelligenceinfo Interest: 🔍 Active Actors: 🔍 Active APT Groups: 🔍 Countermeasuresinfo Recommended: Upgrade Status: 🔍 0-Day Time: 🔒 Upgrade: iCalendar 2.12.2 Patch: b8d23b490363ee5fffaec1d269a8618a912ca265 Timelineinfo 03/23/2026 CVE reserved 03/26/2026 +3 days Advisory disclosed 03/26/2026 +0 days VulDB entry created 03/26/2026 +0 days VulDB entry last update Sourcesinfo Product: github.com Advisory: GHSA-pv9c-9mfh-hvxq Status: Confirmed CVE: CVE-2026-33635 (🔒) GCVE (CVE): GCVE-0-2026-33635 GCVE (VulDB): GCVE-100-353755 Entryinfo Created: 03/26/2026 23:12 Changes: 03/26/2026 23:12 (67) Complete: 🔍 Cache ID: 99:DCC:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸