Security readout for executives and security teams
Plain-English summary
Synapse servers before 1.152.1 can be disrupted in federated Matrix rooms so clients may not show full room history. This is a service reliability issue, not evidence of data theft or account takeover. The fix named in the sources is Synapse 1.152.1.
Executive priority
Treat this as a moderate reliability fix. It can impair collaboration records visible to users, but the provided sources do not indicate data compromise, privilege escalation, or active exploitation. Patch during the next normal maintenance window unless federated rooms are business-critical.
Technical view
CVE-2026-45076 is a CWE-20 input validation issue in Element Synapse before 1.152.1. A malicious homeserver in a federated room can craft events that prevent Synapse from serving complete paginated history to clients. CVSS v4.0 is 5.1, with low availability impact and no stated confidentiality or integrity impact.
Likely exposure
Exposure is limited to organizations running Element Synapse versions earlier than 1.152.1, especially where federation is enabled and users participate in federated rooms. Non-Synapse Matrix servers are not identified as affected in the provided sources.
Exploitation context
The bundle does not cite CISA KEV listing or any active exploitation report. The described attacker is a malicious homeserver in a federated room, and the observable outcome is failed or incomplete room history pagination for clients.
Researcher notes
The public detail is limited to crafted room events affecting pagination in federated rooms. Sources identify the product, fixed version, CWE-20, CVSS vector, and impact class, but do not provide deeper root-cause detail or exploitation telemetry.
Mitigation direction
- Upgrade affected Synapse deployments to version 1.152.1 or later.
- Review the GitHub advisory for any vendor-specific operational guidance.
- Prioritize federated Synapse deployments with high-value or compliance-sensitive rooms.
- Communicate expected user impact: missing or incomplete room history display.
Validation and detection
- Inventory Synapse versions and identify instances below 1.152.1.
- Confirm upgraded servers report Synapse 1.152.1 or later.
- Check whether federation is enabled on affected deployments.
- Review support reports for missing room history or pagination failures.
- After upgrade, validate normal client history pagination in federated rooms.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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CWE-20: Exact CWE lookup
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Open ATT&CK lookupCVE-2026-45076 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.1 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
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.
SSVC decision data
CVSS vector scores
1 official scoreWe 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.
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N——GitHub_MVulnerability scoring details
Base CVSS 4.0 score
5.1MediumVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/element-hq/synapse/security/advisories/GHSA-6qf2-7x63-mm6vCVE reference, GitHub_M · x_refsource_CONFIRM
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.