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Full vulnerability report · 2026
CVE-2026-21876High confidence

OWASP CRS has multipart bypass using multiple content-type parts

coreruleset · coreruleset

Official source article: GitHub GHSA-36FV-25J3-R2C5 ↗. Check the applicable product and release in the original source.

9.3CriticalCVSS 3.1
Recommended action
Within 72 hours

Critical technical impact with a remotely reachable, unauthenticated path and a public exploit reference; no CISA KEV confirmation is currently recorded.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityCriticalOperational priority:Critical, unchanged from published severity.unchanged

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 17.88% 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 coreruleset coreruleset 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.

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
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 · sourcemodsecurity-crsVendor fix publishedDebian records a fixed source-package version for this release.3.3.7-1+deb13u1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcemodsecurity-crsVendor fix publishedDebian records a fixed source-package version for this release.3.3.4-1+deb12u1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcemodsecurity-crsVendor fix publishedDebian records a fixed source-package version for this release.3.3.8-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcemodsecurity-crsVendor fix publishedDebian records a fixed source-package version for this release.3.3.8-1Debian Security Tracker ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivemodsecurity-crsUnder 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
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-2026-1669

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

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
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 72 hours

Critical technical impact with a remotely reachable, unauthenticated path and a public exploit reference; no CISA KEV confirmation is currently recorded.

Patch available
01

What, why and how

The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 4.22.0 and 3.3.8, the current rule 922110 has a bug when processing multipart requests with multiple parts. When the first rule in a chain iterates over a collection (like `MULTIPART_PART_HEADERS`), the capture variables (`TX:0`, `TX:1`) get overwritten with each iteration. Only the last captured value is available to the chained rule, which means malicious charsets in earlier parts can be missed if a later part has a legitimate charset. Versions 4.22.0 and 3.3.8 patch the issue.

What

The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 4.22.0 and 3.3.8, the current rule 922110 has a bug when processing multipart requests with multiple parts. When the first rule in a chain iterates over a collection (like `MULTIPART_PART_HEADERS`), the capture variables (`TX:0`, `TX:1`) get overwritten with each iteration. Only the last captured value is available to the chained rule, which means malicious charsets in earlier parts can be missed if a later part has a legitimate charset. Versions 4.22.0 and 3.3.8 patch the issue.

Why

The product receives data from an upstream component, but does not filter all instances of a special element before sending it to a downstream component.

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

The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 4.22.0 and 3.3.8, the current rule 922110 has a bug when processing multipart requests with multiple parts. When the first rule in a chain iterates over a collection (like `MULTIPART_PART_HEADERS`), the capture variables (`TX:0`, `TX:1`) get overwritten with each iteration. Only the last captured value is available to the chained rule, which means malicious charsets in earlier parts can be missed if a later part has a legitimate charset. Versions 4.22.0 and 3.3.8 patch the issue.

Why

The product receives data from an upstream component, but does not filter all instances of a special element before sending it to a downstream component.

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

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
a network path → Incomplete Filtering of Multiple Instances of Special Elements → 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
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-794 ↗

CWE-794: Incomplete Filtering of Multiple Instances of Special Elements. The product receives data from an upstream component, but does not filter all instances of a special element before sending it to a downstream component.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N

Common Vulnerability Scoring System 3.1: 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.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SChangedScope: The attack can affect a component governed by a different security authority.CHighConfidentiality impact: A successful attack can cause a major loss.ILowIntegrity impact: A successful attack can cause a limited loss.ANoneAvailability impact: 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-794Public exploit reference
A

Official authority intelligence

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

BSI · German · WID-SEC-2026-1185Kemp LoadMaster und Progress Software MOVEit WAF: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Kemp LoadMaster und Progress Software MOVEit WAF ausnutzen, um beliebigen Programmcode auszuführen oder Sicherheitsmaßnahmen zu umgehen.

Official advisory ↗
Canadian Centre for Cyber Security · English · AV26-371Progress security advisory (AV26-371)

On April 20, 2026, Progress published security advisories to address vulnerabilities in the following products:

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260114Security Bulletin 14 Jan 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 14 Jan 2026, published on 14 January 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-014248Progress Software CorporationのConnection Manager for ObjectScale等の複数製品におけるコマンドインジェクションの脆弱性

Progress ADC製品のAPIにおけるOSコマンドインジェクションのリモートコード実行の脆弱性により、「Geo Administration」権限を持つ認証済み攻撃者は、'addcountry'コマンドの未検証入力を悪用してLoadMasterアプライアンス上で任意のコマンドを実行できます。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-014247Progress Software CorporationのConnection Manager for ObjectScale等の複数製品におけるコマンドインジェクションの脆弱性

Progress ADC製品のAPIには、OSコマンドインジェクションによるリモートコード実行の脆弱性があります。この脆弱性により、「All」権限を持つ認証済み攻撃者が、'killsession'コマンド内のサニタイズされていない入力を悪用し、LoadMasterアプライアンス上で任意のコマンドを実行できる可能性があります。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-014246Progress Software CorporationのConnection Manager for ObjectScale等の複数製品におけるコマンドインジェクションの脆弱性

Progress ADC製品のAPIにおけるOSコマンドインジェクションのリモートコード実行の脆弱性により、「VS Administration」権限を持つ認証済みの攻撃者が、'aclcontrol'コマンドの未検証の入力を悪用し、LoadMasterアプライアンス上で任意のコマンドを実行できます。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-014238Progress Software CorporationのConnection Manager for ObjectScale等の複数製品におけるコマンドインジェクションの脆弱性

UIにおけるOSコマンドインジェクションによるリモートコード実行の脆弱性がProgress ADC製品に存在します。この脆弱性により、「All」権限を持つ認証済み攻撃者がファイルアップロードプロセス中に、カスタムWAFルールファイルの未検証の入力を悪用して、LoadMasterアプライアンス上で任意のコマンドを実行できます。

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-004742OWASPのOWASP ModSecurity Core Rule Set (CRS)における特殊要素の複数インスタンスのフィルタリングに関する脆弱性

OWASPコアルールセット（CRS）は、互換性のあるウェブアプリケーションファイアウォールで使用される汎用的な攻撃検出ルールのセットです。バージョン4.22.0および3.3.8以前には、現在のルール922110でマルチパートリクエストの複数パーツを処理する際にバグが存在しました。チェーン内の最初のルールがコレクション（例えば`MULTIPART_PART_HEADERS`）を反復処理すると、キャプチャ変数（`TX:0`、`TX:1`）が各反復で上書きされます。そのため、チェーンされたルールで使用可能なのは最後にキャプチャされた値のみであり、後のパーツに正当な文字セットがある場合、前のパーツの悪意のある文字セットを見逃す可能性がありました。この問題はバージョン4.22.0および3.3.8で修正されています。

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.
Patch available
Affected
coreruleset: < 4.22.0, < 3.3.8
Fixed
An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
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 8 Jan 2026 · Last source change 9 Apr 2026, 15:41 UTC · CWE-794 · Incomplete Filtering of Multiple Instances of Special Elements

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-2026-1669
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD modified after enrichment

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

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-1669↗Public exploit reference · GitHub GHSA-36FV-25J3-R2C5↗Patch or update reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
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-2026-21876 · cve.blacktree.nl