CVE-2020-11100 – This vulnerability allows remote attackers to w... (How to Fix)

Q: What is the severity of CVE-2020-11100?

CVE-2020-11100 has a CVSS score of 8.8 (HIGH). This vulnerability allows remote attackers to write arbitrary bytes to heap memory via a crafted HTTP/2 request to HAProxy's HPACK decoder. Successful exploitation could lead to remote code execution, denial of service, or information disclosure. Affects HAProxy 1.8 through 2.x before version 2.1.4.

📋 TL;DR

This vulnerability allows remote attackers to write arbitrary bytes to heap memory via a crafted HTTP/2 request to HAProxy's HPACK decoder. Successful exploitation could lead to remote code execution, denial of service, or information disclosure. Affects HAProxy 1.8 through 2.x before version 2.1.4.

💻 Affected Systems

Products:

HAProxy

Versions: 1.8 through 2.x before 2.1.4

Operating Systems: Linux, BSD, Other Unix-like systems

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects configurations using HTTP/2. HTTP/1.x configurations are not vulnerable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the privileges of the HAProxy process, potentially leading to complete system compromise.

🟠

Likely Case

Denial of service through process crashes or memory corruption, disrupting load balancing services.

🟢

If Mitigated

Limited impact if proper network segmentation and least privilege principles are applied.

🌐 Internet-Facing: HIGH - HAProxy is typically deployed as an internet-facing reverse proxy/load balancer, making it directly accessible to attackers.

🏢 Internal Only: MEDIUM - Internal HAProxy instances could still be targeted by compromised internal systems or lateral movement.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploit requires crafting specific HTTP/2 requests to trigger the heap corruption. Public proof-of-concept code exists.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 2.1.4 and later

Vendor Advisory: http://www.haproxy.org

Restart Required: Yes

Instructions:

1. Download HAProxy 2.1.4 or later from haproxy.org. 2. Compile and install the new version. 3. Replace the existing HAProxy binary. 4. Restart HAProxy service.

🔧 Temporary Workarounds

Disable HTTP/2

all

Disable HTTP/2 support in HAProxy configuration to prevent exploitation.

In HAProxy config, ensure no 'alpn h2' or similar HTTP/2 directives are present.

🧯 If You Can't Patch

Implement network segmentation to restrict access to HAProxy instances.
Deploy web application firewall (WAF) rules to detect and block malicious HTTP/2 traffic.

🔍 How to Verify

Check if Vulnerable:

Check HAProxy version with 'haproxy -v' and verify it's below 2.1.4 and at least 1.8.

Check Version:

haproxy -v

Verify Fix Applied:

After patching, run 'haproxy -v' and confirm version is 2.1.4 or higher.

📡 Detection & Monitoring

Log Indicators:

Unexpected HAProxy process crashes
Memory corruption errors in system logs

Network Indicators:

Malformed HTTP/2 requests with unusual header patterns

SIEM Query:

source="haproxy.log" AND ("segmentation fault" OR "memory corruption" OR "invalid write")

📊 Metadata

CVE ID: CVE-2020-11100

CVSS v3 Score: 8.8 (HIGH)

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

CWE: CWE-787

Published: April 2, 2020

Last Updated: November 21, 2024

🔗 References

http://lists.opensuse.org/opensuse-security-announce/2020-04/msg00002.html Mailing List,Third Party Advisory
http://packetstormsecurity.com/files/157323/haproxy-hpack-tbl.c-Out-Of-Bounds-Write.html Third Party Advisory,VDB Entry
http://www.haproxy.org Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1819111 Issue Tracking,Third Party Advisory
https://bugzilla.suse.com/show_bug.cgi?id=1168023 Issue Tracking,Third Party Advisory
https://git.haproxy.org/?p=haproxy.git%3Ba=commit%3Bh=5dfc5d5cd0d2128d77253ead3acf03a421ab5b88
https://lists.debian.org/debian-security-announce/2020/msg00052.html Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/264C7UL3X7L7QE74ZJ557IOUFS3J4QQC/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MNW5RZLIX7LOXRLV7WMHX22CI43XSXKW/
https://security.gentoo.org/glsa/202012-22 Third Party Advisory
https://usn.ubuntu.com/4321-1/ Third Party Advisory
https://www.debian.org/security/2020/dsa-4649 Third Party Advisory
https://www.haproxy.org/download/2.1/src/CHANGELOG Release Notes,Vendor Advisory
https://www.mail-archive.com/haproxy%40formilux.org/msg36876.html
http://lists.opensuse.org/opensuse-security-announce/2020-04/msg00002.html Mailing List,Third Party Advisory
http://packetstormsecurity.com/files/157323/haproxy-hpack-tbl.c-Out-Of-Bounds-Write.html Third Party Advisory,VDB Entry
http://www.haproxy.org Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1819111 Issue Tracking,Third Party Advisory
https://bugzilla.suse.com/show_bug.cgi?id=1168023 Issue Tracking,Third Party Advisory
https://git.haproxy.org/?p=haproxy.git%3Ba=commit%3Bh=5dfc5d5cd0d2128d77253ead3acf03a421ab5b88
https://lists.debian.org/debian-security-announce/2020/msg00052.html Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/264C7UL3X7L7QE74ZJ557IOUFS3J4QQC/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MNW5RZLIX7LOXRLV7WMHX22CI43XSXKW/
https://security.gentoo.org/glsa/202012-22 Third Party Advisory
https://usn.ubuntu.com/4321-1/ Third Party Advisory
https://www.debian.org/security/2020/dsa-4649 Third Party Advisory
https://www.haproxy.org/download/2.1/src/CHANGELOG Release Notes,Vendor Advisory
https://www.mail-archive.com/haproxy%40formilux.org/msg36876.html

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