HighCVE-2026-54873

QUIC STREAM Fragment Metadata DoS (CVE-2026-54873)

Published 29.09.2026Last modified 08.10.2026Sources: Red Hat, Debian, CVE.org, Ubuntu, EUVD, Msrc Update Guide, BSI

What is affected, what to do

A flaw was found in OpenSSL. A remote attacker can cause a Denial of Service (DoS) by sending specially crafted network packets to a QUIC protocol endpoint.

Update OpenSSL to version 4.0.3, OpenSSL to version 3.6.5, OpenSSL to version 3.5.9.

Affected: OpenSSL lt 4.0.0..4.0.3
OpenSSL lt 3.6.0..3.6.5
OpenSSL lt 3.5.0..3.5.9
OpenSSL lt 3.4.0..3.4.8
Fixed in: OpenSSL 4.0.3
OpenSSL 3.6.5
OpenSSL 3.5.9
OpenSSL 3.4.8

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Metrics

7.5

XIEM Effective CVSS

Highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v3

7.5

CVSS v3

Severity High on the scale from 0 to 10.

Source: Red Hat, Debian, CVE.org, Ubuntu, EUVD, Msrc Update Guide, BSI

0.7 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 54.5

Show all metrics

Severity: High
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 88.37 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 7.5 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.5
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.7 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 54.5; High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 29.09.2026
CISA assessment (SSVC): Exploitation: none known · automatable · Technical impact: partial; Source: CISA Vulnrichment, as of 30 September 2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-770

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

A flaw was found in OpenSSL. A remote attacker can cause a Denial of Service (DoS) by sending specially crafted network packets to a QUIC protocol endpoint. Because the QUIC stack retains memory in packet buffers until the receiving application reads the stream data, an attacker can manipulate data transfers to keep these buffers allocated indefinitely. This behavior leads to excessive memory consumption and can exhaust available system resources.

Source: redhat_csaf, Debian Security Advisories, cvelistv5, NVD (NIST), Ubuntu Security Notices, ENISA EUVD, Microsoft Security Update Guide, BSI WID Portal, BSI CSAF

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
OpenSSL	OpenSSL	`3.4.0 – < 3.4.8` `3.5.0 – < 3.5.9` `3.6.0 – < 3.6.5` `4.0.0 – < 4.0.3`	`3.4.8` `3.5.9` `3.6.5` `4.0.3`
openssl	openssl	`4.0.0 – < 4.0.3` `3.5.0 – < 3.5.9` `3.6.0 – < 3.6.5` `3.4.0 – < 3.4.8`	`4.0.3` `3.5.9` `3.6.5` `3.4.8`

Vendors and products

Affected operating systems

Affected operating systems

Linux	debian	openssl	`trixie`

Weakness classes (CWE)

CWE-770Allocation of Resources Without Limits or Throttling
Base
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Entry at MITRE CWE-770

References & sources

openssl-library.orgOpenSSL AdvisoryVendor advisory, euvd
github.com4.0.3 git commitPatch, euvd
github.com3.6.5 git commitPatch, euvd
github.com3.5.9 git commitPatch, euvd
github.com3.4.8 git commitPatch, euvd

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

08.10.2026Initial analysis by NVDNVD

Newly listed as affected:

OpenSSL (3.4.0 – before 3.4.8; 3.5.0 – before 3.5.9; 3.6.0 – before 3.6.5; 4.0.0 – before 4.0.3)

New references:

and 1 more reference

Show 6 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Product configuration	added	—	OR cpe:2.3:a:openssl:openssl::::::::* versions from (including) 3.4.0 up to (excluding) 3.4.8 cpe:2.3:a:openssl:openssl::::::::* versions from (including) 3.5.0 up to (excluding) 3.5.9 cpe:2.3:a:openssl:openssl::::::::* versions from (including) 3.6.0 up to (excluding) 3.6.5 cpe:2.3:a:openssl:openssl::::::::* versions from (including) 4.0.0 up to (excluding) 4.0.3
Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/1f643b8bc735487b500a1f68a7fb3a22d5e38e23 Types: Patch
Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/279e7ee1392af98785746788168749491c74bd53 Types: Patch
Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/3ea6213e050e938ecbbf8c4eff32bec2736780eb Types: Patch
Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/7127fb10888b49711c63128a09e524c0d2d5d0b2 Types: Patch
Reference type	added	—	OpenSSL Software Foundation: https://openssl-library.org/news/secadv/20260929.txt Types: Vendor Advisory

Source identifier: nvd@nist.gov

30.09.2026Record modifiedCISA ADP

CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CISA assessment (SSVC): exploitation: none known, automatable: yes

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
CVSS	added	—	AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
SSVC assessment	added	—	{"id":"CVE-2026-54873","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-30T19:18:10.966747Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

29.09.2026Receivedopenssl.org

Weakness type: CWE-770

Description added or changed

New references:

and 1 more reference

Show 8 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	Issue summary: QUIC process may keep memory for QUIC packet buffer for much longer period than necessary. Impact summary: Remote peer can exploit this vulnerability by sending maliciously crafted packets, making the local QUIC stack to keep the memory for packet buffers allocated. The time for which the memory remains allocated is entirely under the control of the potentially malicious remote peer. CWE: CWE-770: Allocation of Resources Without Limits or Throttling Description: To save copy operation from the packet buffer to the stream reassemble buffer the QUIC stack leaves the stream data on the packet buffer waiting to be copied to a buffer provided by the local receiving application. The QUIC stack releases a reference to the packet buffer only after the data are copied to the application buffer. This design is more efficient for legitimate data transfers but enables an attacker to allocate a lot more memory than actually required by the data kept in the receiving stream buffer. To mitigate the vulnerability, the QUIC stack now calculates and monitors memory overhead for every stream. The memory overhead for a single stream frame is calculated as a difference between the size of the whole packet that carries the stream frame and the size of the stream frame itself. The memory overhead for a single stream frame is added to the total (cumulative) memory overhead QUIC stack keeps for each stream. Once the cumulative memory overhead exceeds 64kB, the QUIC stack moves the stream frame data from the packet buffer to the stream buffer, starting with the next packet received. FIPS impact: no The FIPS module is not affected as the QUIC implementation is outside of the OpenSSL FIPS module boundary.
Weakness type (CWE)	added	—	CWE-770
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/54xxx/CVE-2026-54873.json">CVE-2026-54873</a>
Reference	added	—	https://github.com/openssl/openssl/commit/1f643b8bc735487b500a1f68a7fb3a22d5e38e23
Reference	added	—	https://github.com/openssl/openssl/commit/279e7ee1392af98785746788168749491c74bd53
Reference	added	—	https://github.com/openssl/openssl/commit/3ea6213e050e938ecbbf8c4eff32bec2736780eb
Reference	added	—	https://github.com/openssl/openssl/commit/7127fb10888b49711c63128a09e524c0d2d5d0b2
Reference	added	—	https://openssl-library.org/news/secadv/20260929.txt

Source identifier: openssl-security@openssl.org

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