CVE-2020-9490
📋 TL;DR
This vulnerability in Apache HTTP Server allows an attacker to cause a denial-of-service (crash) by sending a specially crafted Cache-Digest header in an HTTP/2 request, followed by an HTTP/2 PUSH operation. It affects Apache HTTP Server versions 2.4.20 through 2.4.43 with HTTP/2 enabled. Organizations running vulnerable Apache configurations with HTTP/2 support are at risk.
💻 Affected Systems
- Apache HTTP Server
📦 What is this software?
Communications Session Report Manager by Oracle
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Communications Session Route Manager by Oracle
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Enterprise Linux For Ibm Z Systems by Redhat
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Enterprise Linux For Ibm Z Systems Eus by Redhat
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Enterprise Linux For Ibm Z Systems Eus by Redhat
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Enterprise Linux For Ibm Z Systems Eus by Redhat
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Enterprise Linux For Ibm Z Systems Eus by Redhat
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Enterprise Linux For Power Little Endian by Redhat
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Enterprise Linux For Power Little Endian Eus by Redhat
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Enterprise Linux For Power Little Endian Eus by Redhat
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Enterprise Linux For Power Little Endian Eus by Redhat
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Enterprise Linux For Power Little Endian Eus by Redhat
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Enterprise Linux Server Update Services For Sap Solutions by Redhat
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Enterprise Linux Server Update Services For Sap Solutions by Redhat
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Enterprise Linux Server Update Services For Sap Solutions by Redhat
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Fedora by Fedoraproject
Fedora by Fedoraproject
Hyperion Infrastructure Technology by Oracle
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Leap by Opensuse
Leap by Opensuse
Openstack by Redhat
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
⚠️ Risk & Real-World Impact
Worst Case
Complete server crash leading to denial-of-service for all hosted websites and applications, potentially requiring manual restart and causing extended downtime.
Likely Case
Targeted denial-of-service attacks against specific Apache servers, causing service disruption until the server is restarted.
If Mitigated
Minimal impact if HTTP/2 PUSH is disabled or the server is patched; normal operations continue unaffected.
🎯 Exploit Status
Exploit requires HTTP/2 access and knowledge of server configuration; public proof-of-concept code exists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.4.44 and later
Vendor Advisory: https://httpd.apache.org/security/vulnerabilities_24.html#CVE-2020-9490
Restart Required: Yes
Instructions:
1. Download Apache HTTP Server version 2.4.44 or later from the official Apache website. 2. Backup current configuration files. 3. Stop the Apache service. 4. Install the updated version. 5. Restore configuration files. 6. Start the Apache service.
🔧 Temporary Workarounds
Disable HTTP/2 PUSH
allPrevents the vulnerable code path by disabling HTTP/2 PUSH functionality.
Add 'H2Push off' to your Apache configuration file (httpd.conf or appropriate virtual host file)
Disable HTTP/2 Entirely
allCompletely disables HTTP/2 protocol support, eliminating the vulnerability.
Remove or comment out 'Protocols h2 http/1.1' from your Apache configuration
🧯 If You Can't Patch
- Implement network-level controls to block or rate-limit HTTP/2 traffic to vulnerable servers
- Deploy web application firewall (WAF) rules to detect and block malicious Cache-Digest headers
🔍 How to Verify
Check if Vulnerable:
Check Apache version with 'httpd -v' or 'apache2 -v' and verify if HTTP/2 is enabled in configuration files.Check Version:
httpd -v # or apache2 -v on Debian-based systemsVerify Fix Applied:
Confirm Apache version is 2.4.44 or later and test HTTP/2 functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Apache crash logs, segmentation fault errors in error_log
- Unusual HTTP/2 connection attempts with Cache-Digest headers
Network Indicators:
- HTTP/2 traffic patterns with Cache-Digest headers followed by connection resets
SIEM Query:
source="apache_error_log" AND ("segmentation fault" OR "crash" OR "SIGSEGV")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00068.html
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00071.html
- http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00081.html
- http://packetstormsecurity.com/files/160392/Apache-2.4.43-mod_http2-Memory-Corruption.html
- https://httpd.apache.org/security/vulnerabilities_24.html#CVE-2020-9490
- https://lists.apache.org/thread.html/r06f0d87ebb6d59ed8379633f36f72f5b1f79cadfda72ede0830b42cf%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r09bb998baee74a2c316446bd1a41ae7f8d7049d09d9ff991471e8775%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r0b6541c5fb2f8fb383861333400add7def625bc993300300de0b4f8d%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r3c5c3104813c1c5508b55564b66546933079250a46ce50eee90b2e36%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r5debe8f82728a00a4a68bc904dd6c35423bdfc8d601cfb4579f38bf1%40%3Cdev.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r623de9b2b2433a87f3f3a15900419fc9c00c77b26936dfea4060f672%40%3Cdev.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r97d0faab6ed8fd0d439234b16d05d77b22a07b0c4817e7b3cca419cc%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r9e485ce5a01c9dc3d4d785a7d28aa7400ead1e81884034ff1f03cfee%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r9e9f1a7609760f0f80562eaaec2aa3c32d525c3e0fca98b475240c71%40%3Cdev.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/ra4da876037477c06f2677d7a1e10b5a8613000fca99c813958070fe9%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rdf3e5d0a5f5c3d90d6013bccc6c4d5af59cf1f8c8dea5d9a283d13ce%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rf6449464fd8b7437704c55f88361b66f12d5b5f90bcce66af4be4ba9%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rfed9fea918e090383da33e393eb6c2755fccf05032bd7d6eb4737c9e%40%3Ccvs.httpd.apache.org%3E
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4NKWG2EXAQQB6LMLATKZ7KLSRGCSHVAN/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ITVFDBVM6E3JF3O7RYLRPRCH3RDRHJJY/
- https://security.gentoo.org/glsa/202008-04
- https://security.netapp.com/advisory/ntap-20200814-0005/
- https://usn.ubuntu.com/4458-1/
- https://www.debian.org/security/2020/dsa-4757
- https://www.oracle.com/security-alerts/cpujan2021.html
- https://www.oracle.com/security-alerts/cpuoct2020.html
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00068.html
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00071.html
- http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00081.html
- http://packetstormsecurity.com/files/160392/Apache-2.4.43-mod_http2-Memory-Corruption.html
- https://httpd.apache.org/security/vulnerabilities_24.html#CVE-2020-9490
- https://lists.apache.org/thread.html/r06f0d87ebb6d59ed8379633f36f72f5b1f79cadfda72ede0830b42cf%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r09bb998baee74a2c316446bd1a41ae7f8d7049d09d9ff991471e8775%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r0b6541c5fb2f8fb383861333400add7def625bc993300300de0b4f8d%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r3c5c3104813c1c5508b55564b66546933079250a46ce50eee90b2e36%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r5debe8f82728a00a4a68bc904dd6c35423bdfc8d601cfb4579f38bf1%40%3Cdev.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r623de9b2b2433a87f3f3a15900419fc9c00c77b26936dfea4060f672%40%3Cdev.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r97d0faab6ed8fd0d439234b16d05d77b22a07b0c4817e7b3cca419cc%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r9e485ce5a01c9dc3d4d785a7d28aa7400ead1e81884034ff1f03cfee%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r9e9f1a7609760f0f80562eaaec2aa3c32d525c3e0fca98b475240c71%40%3Cdev.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/ra4da876037477c06f2677d7a1e10b5a8613000fca99c813958070fe9%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rdf3e5d0a5f5c3d90d6013bccc6c4d5af59cf1f8c8dea5d9a283d13ce%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rf6449464fd8b7437704c55f88361b66f12d5b5f90bcce66af4be4ba9%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rfed9fea918e090383da33e393eb6c2755fccf05032bd7d6eb4737c9e%40%3Ccvs.httpd.apache.org%3E
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4NKWG2EXAQQB6LMLATKZ7KLSRGCSHVAN/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ITVFDBVM6E3JF3O7RYLRPRCH3RDRHJJY/
- https://security.gentoo.org/glsa/202008-04
- https://security.netapp.com/advisory/ntap-20200814-0005/
- https://usn.ubuntu.com/4458-1/
- https://www.debian.org/security/2020/dsa-4757
- https://www.oracle.com/security-alerts/cpujan2021.html
- https://www.oracle.com/security-alerts/cpuoct2020.html
