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Full vulnerability report · 2026
CVE-2026-49851High confidence

Mistune: Potential DoS via quadratic-time parsing in parse_link_text

lepture · mistune

Official source article: GitHub GHSA-QCQ2-496W-V96P ↗. Check the applicable product and release in the original source.

8.7HighCVSS 4.0
Recommended action
Patch only the product branches with a verified fix

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 3 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 28 Aug 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • A structured source references public exploit or proof-of-concept material.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 0.63% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs lepture mistune and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 3 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

5 package states
Package result overrides the generic status

BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 3 affected package states shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.

Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcemistuneAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcemistuneNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcemistuneAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcemistuneAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivemistuneUnder evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Open-source package ranges2 source-attributed ranges

These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.

Ecosystem and packageAffected rangeFirst fixed versionEvidence
PyPImistuneECOSYSTEM: introduced 0; fixed 3.3.03.3.0OSV record ↗aggregator derived · 10 Sep 2026
pipmistune< 3.3.03.3.0GitHub advisory ↗upstream repository advisory · 9 Jul 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

2 current
CVE-2026-49851 · CSAF 2.0 · revision 2 · interimSUSE Product Security TeamCVE-2026-49851
37 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • python-mistune as component of SUSE Linux Enterprise Desktop 15 SP7
  • python311-mistune as component of SUSE Linux Enterprise Desktop 15 SP7
  • python-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS
  • python311-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS
  • python-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP4
  • python311-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP4
  • python-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS
  • python311-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS
  • python-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP5
  • python311-mistune as component of SUSE Linux Enterprise High Performance Computing 15 SP5
  • python-mistune as component of SUSE Linux Enterprise Module for Package Hub 15 SP7
  • python3-mistune as component of SUSE Linux Enterprise Module for Package Hub 15 SP7
Summary
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n^2)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.
Remediation
To install this SUSE Security Update use the SUSE recommended installation methods like YaST online_update or "zypper patch".
CVE-2026-49851 · CSAF 2.0 · revision 3 · finalRed Hat Product SecurityMistune: Mistune: Denial of Service via crafted Markdown input
1 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
Summary
A flaw was found in Mistune, a Python Markdown parser. A remote attacker can exploit this vulnerability by providing a specially crafted Markdown input containing many consecutive bracket characters. This can lead to excessive CPU usage, causing a denial-of-service (DoS) condition on the affected system.
Remediation
For Red Hat OpenShift AI 3.4.4 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-39007

No EUVD known-exploited evidence

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
8.7 · CVSS 4.0
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 3 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

What

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

Why

The product does not properly control the allocation and maintenance of a limited resource.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

Why

The product does not properly control the allocation and maintenance of a limited resource.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

CISA Vulnrichment records proof-of-concept exploitation in its SSVC data. BlackTree has not independently executed or validated exploit material.

Likely attack path
a network path → Uncontrolled Resource Consumption → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-400 ↗

CWE-400: Uncontrolled Resource Consumption. The product does not properly control the allocation and maintenance of a limited resource.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATNoneAttack requirements: No additional deployment or execution condition is required.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VINoneVulnerable-system integrity: No direct loss is represented by this metric.VAHighVulnerable-system availability: A successful attack can cause a major loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-400Public exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-39007Official EUVD mapping

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

Official EUVD record ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260701Security Bulletin 1 July 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 1 July 2026, published on 1 July 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-1206Multiples vulnérabilités dans les produits IBM

d?id=CVE-2026-48710 Référence CVE CVE-2026-48735 https://www.cve.org/CVERecord?id=CVE-2026-48735 Référence CVE CVE-2026-48817 https://www.cve.org/CVERecord?id=CVE-2026-48817 Référence CVE CVE-2026-48818 https://www.cve.org/CVERecord?id=CVE-2026-48818 Référence CVE CVE-2026-49460 https://www.cve.org/CVERecord?id=CVE-2026-49460 Référence CVE CVE-2026-49461 https://www.cve.org/CVERecord?id=CVE-2026-49461 Référence CVE CVE-2026-49476 https://www.cve.org/CVERecord?id=CVE-2026-49476 Référence CVE CVE-2026-49477 https://www.cve.org/CVERecord?id=CVE-2026-49477 Référence CVE CVE-2026-49844 https://www.cve.org/CVERecord?id=CVE-2026-49844 Référence CVE CVE-2026-49851 https://www.cve.org/CVERecord?id=CVE-2026-49851 Référence CVE CVE-2026-50010 https://www.cve.org/CVERecord?id=CVE-2026-50010 Référence CVE CVE-2026-50011 https://www.cve.org/CVERecord?id=CVE-2026-50011 Référence CVE CVE-2026-50020 https://www.cve.org/CVERecord?id=CVE-2026-50020 Référence CVE CVE-2026-50560 https://www.cve.org/CVERecord?id=CVE-2026-50560 Référence CVE CVE-2026-50645 https://www.cve.org/CVERecord?id=CVE-2026-50645 Référence CVE CVE-2026-50734 https://www.cve.org/CVERecord?id=CVE-2026-50734 Référence CVE CVE-2026-53537 https://www.cve.org/CVERecord?id=CVE-2026-53537 Référence CVE CVE-2026-53538 https://www.cve.org/CVERecord?id=

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix availability varies by product
Affected
Fixed
RHSA-2026:60520: Red Hat OpenShift AI 3.4
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 24 Jun 2026 · Last source change 28 Aug 2026, 12:04 UTC · CWE-400 · Uncontrolled Resource Consumption

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-39007
Product sourceVendor CSAF · SUSE Product Security Team
Remediation sourceVendor CSAF · SUSE Product Security Team
CWE sourceCNA
NVD statusNVD not scheduled

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: removed vendor advisory: access.redhat.com/RHSA-2026:60520.
    Before
    vendor advisory: access.redhat.com/RHSA-2026:60520
    After
    no authoritative guidance recorded
    CNA ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added vendor advisory: access.redhat.com/RHSA-2026:60520.
    Before
    no authoritative guidance recorded
    After
    vendor advisory: access.redhat.com/RHSA-2026:60520
    access.redhat.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    < 3.3.0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    < 3.3.0 · Fixed: For Red Hat OpenShift AI 3.4.4 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
    Red Hat Product Security ↗
  4. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    Red Hat Product Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-49851 · cve.blacktree.nl