CVE-2023-44487
CVE-2023-44487 is a security flaw in IETF HTTP/2. Attackers can crash IETF HTTP/2 or stop it working. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 10 Oct 2023.[1]
IETF HTTP/2 is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version V3.0 of SINEC NMS.
Description
CISA calls it a rapid reset attack in IETF HTTP/2. In its words: “HTTP/2 contains a rapid reset vulnerability that allows for a distributed denial-of-service attack (DDoS).”[1]
The CVE record adds: “The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.”[2]
The underlying weakness is resource exhaustion (CWE-400), in MITRE’s list of common software weaknesses.
It scores 7.5 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists one fixed version: everything before it is affected.[2]
| Product | Fixed in |
|---|---|
| SINEC NMS | V3.0 |
Most families won’t have IETF HTTP/2; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 10 Oct 2023, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 31 Oct 2023 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at over 99%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
IETF has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.IETF HTTP/2 is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version V3.0 of SINEC NMS), or not in use. CISA gave US government agencies until 31 Oct 2023 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.5.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at over 99%.[4] |
See also
Other IETF flaws
- CVE-2023-29552, IETF Service Location Protocol (SLP): denial-of-service ·
Other resource exhaustion flaws
- CVE-2026-28318, SolarWinds Serv-U: uncontrolled resource consumption ·
- CVE-2026-45498, Microsoft Defender: denial of service ·
- CVE-2023-38180, Microsoft .NET Core and Visual Studio: denial-of-service ·
- CVE-2004-1464, Cisco IOS: denial-of-service ·
- CVE-2020-3569, Cisco IOS XR: software DVMRP memory exhaustion ·
Added the same day
- CVE-2023-41763, Microsoft Skype for Business: privilege escalation ·
- CVE-2023-36563, Microsoft WordPad: information disclosure ·
- CVE-2023-21608, Adobe Acrobat and Reader: use-after-free ·
- CVE-2023-20109, Cisco IOS and IOS XE: group encrypted transport VPN out-of-bounds write ·
References
- ^ Cybersecurity and Infrastructure Security Agency. “HTTP/2 Rapid Reset Attack Vulnerability”. Known Exploited Vulnerabilities Catalog, added 10 Oct 2023.
- ^ National Institute of Standards and Technology. “CVE-2023-44487 Detail”. National Vulnerability Database, published 10 Oct 2023.
- ^ IETF. Advisories and fixes: blog.cloudflare.com, access.redhat.com, blog.cloudflare.com, blog.litespeedtech.com, blog.vespa.ai, and 3 more on NVD’s record.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 1.000, percentile 100.0, 31 Oct 2026.
- CVE Program. “CVE-2023-44487”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.