CVE-2016-2851 – CVE-2016-2851 is an integer overflow vulnerabil... (How to Fix)

Q: What is the severity of CVE-2016-2851?

CVE-2016-2851 has a CVSS score of 9.8 (CRITICAL). CVE-2016-2851 is an integer overflow vulnerability in libotr's proto.c that allows remote attackers to trigger a heap-based buffer overflow via specially crafted OTR messages. This can lead to denial of service (application crash) or remote code execution. Affects libotr users on 64-bit platforms who process OTR messages.

📋 TL;DR

CVE-2016-2851 is an integer overflow vulnerability in libotr's proto.c that allows remote attackers to trigger a heap-based buffer overflow via specially crafted OTR messages. This can lead to denial of service (application crash) or remote code execution. Affects libotr users on 64-bit platforms who process OTR messages.

💻 Affected Systems

Products:

libotr

Versions: All versions before 4.1.1

Operating Systems: Linux, Unix-like systems with 64-bit architectures

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects 64-bit platforms; 32-bit systems are not vulnerable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the privileges of the vulnerable application, potentially leading to full system compromise.

🟠

Likely Case

Denial of service through application crashes, disrupting OTR-protected communications.

🟢

If Mitigated

Limited impact if patched or if OTR message processing is restricted to trusted sources.

🌐 Internet-Facing: HIGH - Remote attackers can exploit this without authentication via network messages.

🏢 Internal Only: MEDIUM - Requires internal network access but still exploitable without authentication.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending a series of large OTR messages; public proof-of-concept code exists.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 4.1.1

Vendor Advisory: http://lists.opensuse.org/opensuse-security-announce/2016-03/msg00021.html

Restart Required: Yes

Instructions:

1. Update libotr to version 4.1.1 or later using your system's package manager. 2. Restart any applications using libotr (e.g., Pidgin, Adium).

🔧 Temporary Workarounds

Disable OTR messaging

all

Temporarily disable OTR (Off-the-Record) messaging in affected applications to prevent exploitation.

# For Pidgin: Disable OTR in Account Settings > Advanced

Network filtering

linux

Block or filter large OTR messages at network boundaries using firewalls or IDS/IPS.

# Example iptables rule to block large packets (adjust as needed): iptables -A INPUT -p tcp --dport 5222 -m length --length 1000: -j DROP

🧯 If You Can't Patch

Restrict network access to applications using libotr to trusted sources only.
Monitor for crashes or unusual behavior in applications that process OTR messages.

🔍 How to Verify

Check if Vulnerable:

Check libotr version: dpkg -l | grep libotr (Debian/Ubuntu) or rpm -qa | grep libotr (RHEL/CentOS). If version is <4.1.1, it's vulnerable.

Check Version:

dpkg -l | grep libotr  # Debian/Ubuntu; rpm -qa | grep libotr  # RHEL/CentOS; otool -L /path/to/app | grep libotr  # macOS

Verify Fix Applied:

After update, confirm version is >=4.1.1 using the same commands and test OTR functionality.

📡 Detection & Monitoring

Log Indicators:

Application crashes or segmentation faults in logs (e.g., syslog, dmesg) related to libotr or OTR-enabled apps.

Network Indicators:

Unusually large OTR messages or spikes in traffic to OTR-enabled services (e.g., XMPP port 5222).

SIEM Query:

Example: source="syslog" AND ("segmentation fault" OR "crash") AND ("libotr" OR "OTR")

📊 Metadata

CVE ID: CVE-2016-2851

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-119

Published: April 7, 2016

Last Updated: April 12, 2025

🔗 References

http://lists.opensuse.org/opensuse-security-announce/2016-03/msg00021.html Mailing List
http://lists.opensuse.org/opensuse-security-announce/2016-03/msg00030.html Vendor Advisory
http://seclists.org/fulldisclosure/2016/Mar/21 Exploit,Mailing List,Third Party Advisory
http://www.debian.org/security/2016/dsa-3512 Third Party Advisory
http://www.securityfocus.com/archive/1/537745/100/0/threaded Third Party Advisory
http://www.securityfocus.com/bid/84285 Third Party Advisory,VDB Entry
http://www.ubuntu.com/usn/USN-2926-1 Third Party Advisory
https://lists.cypherpunks.ca/pipermail/otr-users/2016-March/002581.html Exploit
https://security.gentoo.org/glsa/201701-10 Third Party Advisory
https://www.exploit-db.com/exploits/39550/ Third Party Advisory,VDB Entry
https://www.x41-dsec.de/lab/advisories/x41-2016-001-libotr/ Exploit
http://lists.opensuse.org/opensuse-security-announce/2016-03/msg00021.html Mailing List
http://lists.opensuse.org/opensuse-security-announce/2016-03/msg00030.html Vendor Advisory
http://seclists.org/fulldisclosure/2016/Mar/21 Exploit,Mailing List,Third Party Advisory
http://www.debian.org/security/2016/dsa-3512 Third Party Advisory
http://www.securityfocus.com/archive/1/537745/100/0/threaded Third Party Advisory
http://www.securityfocus.com/bid/84285 Third Party Advisory,VDB Entry
http://www.ubuntu.com/usn/USN-2926-1 Third Party Advisory
https://lists.cypherpunks.ca/pipermail/otr-users/2016-March/002581.html Exploit
https://security.gentoo.org/glsa/201701-10 Third Party Advisory
https://www.exploit-db.com/exploits/39550/ Third Party Advisory,VDB Entry
https://www.x41-dsec.de/lab/advisories/x41-2016-001-libotr/ Exploit

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