# CVE-2016-5825: libical out-of-bounds read in icalparser_parse_string

Source: https://junglewise.ai/threats/cve-2016-5825-libical-out-of-bounds-read-in-icalparser-parse-string  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2017-01-27. Updated: 2026-05-13  
License: CC BY 4.0 with a link back

CVE-2016-5825 · Severity: medium · CVSS 5.5 · Published 2017-01-27

libical is a widely used open-source library for handling calendar data (iCalendar files). A vulnerability in how it processes calendar files allows an attacker to crash applications that use this library, such as email clients or calendar apps, by sending a specially crafted invitation or calendar file. This results in a denial of service, potentially disrupting scheduling and communication services.

Technologies: [Libical Project Libical](https://junglewise.ai/threats/technologies/libical). Vendors: [Libical Project](https://junglewise.ai/threats/vendors/libical-project).

## Quick answers

**Is CVE-2016-5825 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2016-5825 being exploited in the wild.

**How severe is CVE-2016-5825?** Medium severity, with a CVSS score of 5.5, published 27 January 2017.

**Which products and versions are affected?** Libical Project Libical 0.47, 1.0.

**Is there a fix for CVE-2016-5825?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2016-5825 attacked?** It is attacked over the network or with local access, in a software library.

**Am I affected by CVE-2016-5825?** Check whether you run Libical Project Libical at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A heap-based out-of-bounds read exists in libical versions 0.47 and 1.0 within the icalparser_parse_string function. The root cause is located in the icalmemory_strdup_and_dequote helper function, which fails to properly validate buffer boundaries when processing malformed iCalendar (.ics) files, specifically those with repeated or improperly terminated TZNAME properties. An attacker can exploit this by providing a crafted .ics file to an application linked against libical (such as Mozilla Thunderbird/Lightning). Successful exploitation results in an application crash (SIGSEGV), leading to a denial of service. While the NVD classifies the vector as Local with User Interaction, the practical delivery via email or calendar subscriptions often gives it a remote delivery profile.

## Affected products

- libical project libical 0.47, 1.0

## Timeline

- 2016-06-25: disclosed: Public discussion on oss-security mailing list
- 2017-01-27: advisory: NVD publication date

## References

- [http://www.openwall.com/lists/oss-security/2016/06/25/4](http://www.openwall.com/lists/oss-security/2016/06/25/4)
- [http://www.securityfocus.com/bid/91459](http://www.securityfocus.com/bid/91459)
- [https://bugzilla.mozilla.org/show_bug.cgi?id=1280832](https://bugzilla.mozilla.org/show_bug.cgi?id=1280832)

## Related threats

- [libical out-of-bounds read in icaltime_from_string](https://junglewise.ai/threats/cve-2016-5827-libical-out-of-bounds-read-in-icaltime-from-string)
- [libical out-of-bounds read in parser_get_next_char](https://junglewise.ai/threats/cve-2016-5826-libical-out-of-bounds-read-in-parser-get-next-char)
- [libical use-after-free in iCalendar parsing](https://junglewise.ai/threats/cve-2016-5824-libical-use-after-free-in-icalendar-parsing)
- [libical use-after-free in icalproperty_new_clone](https://junglewise.ai/threats/cve-2016-5823-libical-use-after-free-in-icalproperty-new-clone)
- [libical use-after-free in iCalendar parser](https://junglewise.ai/threats/cve-2016-9584-libical-use-after-free-in-icalendar-parser)