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CVE Record

CVE-2026-33526: Squid vulnerable to Denial of Service in ICP Request handling

Squid is a caching proxy for the Web. Prior to version 7.5, due to heap Use-After-Free, Squid is vulnerable to Denial of Service when handling ICP traffic. This problem allows a remote attacker to perform a reliable and repeatable Denial of Service attack against the Squid service using ICP protocol. This attack is limited to Squid deployments that explicitly enable ICP support (i.e. configure non-zero `icp_port`). This problem _cannot_ be mitigated by denying ICP queries using `icp_access` rules. Version 7.5 contains a patch.

CriticalCVSS 9.2Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

This flaw can let an unauthenticated remote attacker repeatedly crash a Squid proxy, but only where ICP support is explicitly enabled. The issue is severe for affected proxy infrastructure because service availability can be lost without user interaction. Squid 7.5 contains the upstream patch.

Executive priority

Prioritize systems that use Squid as critical proxy infrastructure and have ICP enabled. Treat externally reachable ICP as urgent because the stated impact is reliable service disruption. Where ICP is disabled, urgency is lower but version verification is still required.

Technical view

CVE-2026-33526 is a heap use-after-free in Squid ICP request handling before version 7.5. The CVSS 4.0 score is 9.2. Exposure requires a non-zero icp_port. The advisory states icp_access denial rules do not mitigate the issue.

Likely exposure

Organizations are likely exposed only if they run Squid before 7.5 with ICP explicitly enabled through a non-zero icp_port. Internet-facing or broadly reachable proxy peers increase operational impact. Deployments without ICP enabled are not described as exposed in the provided sources.

Exploitation context

The source bundle supports remote, unauthenticated, reliable denial of service via ICP traffic. It does not show CISA KEV listing or active exploitation evidence. No source in the bundle supports data theft, code execution, or privilege escalation.

Researcher notes

The key exposure condition is configuration-specific: non-zero icp_port. The advisory explicitly rules out icp_access as a sufficient control. Evidence is strongest for denial of service, not confidentiality or integrity compromise. Patch reference points to Squid 7.5.

Mitigation direction

  • Upgrade Squid to version 7.5 or a vendor-fixed package.
  • If ICP is not required, disable ICP by using icp_port 0.
  • Do not rely on icp_access deny rules as mitigation.
  • Review applicable Red Hat errata for packaged platform fixes.
  • Limit ICP reachability to required trusted peers where ICP must remain enabled.

Validation and detection

  • Inventory all Squid deployments and record installed versions.
  • Inspect Squid configuration for non-zero icp_port values.
  • Confirm whether ICP is reachable from untrusted networks.
  • Verify vendor package status against applicable Red Hat advisories.
  • Monitor affected proxies for crashes, restarts, or availability loss.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-416: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · low confidence lookup

CWE-825: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · low confidence lookup

CWE-826: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-33526 mapping review

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.2 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
3ADP providers
18Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.2CVSS 4.0CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H——GitHub_M
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 4.0 score

9.2Critical
CVSS 4.0 vector shape for CVE-2026-33526Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPsquid: Squid: Denial of Service via heap Use-After-Free vulnerability in ICP handling
other:Red Hat severity ratingcvssV3_1
  • 2026-03-26T01:01:16.233Z: Reported to Red Hat.
  • 2026-03-26T00:16:12.195Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
squid-cachesquid< 7.5Listed
Weakness

CWE details

CWE-416CWE-825CWE-826

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-825 · source CWE mapping

Expired Pointer Dereference

Expired Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-826 · source CWE mapping

Premature Release of Resource During Expected Lifetime

Premature Release of Resource During Expected Lifetime represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs