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CVE Record

CVE-2021-34813: Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting t...

Matrix libolm before 3.2.3 allows a malicious Matrix homeserver to crash a client (while it is attempting to retrieve an Olm encrypted room key backup from the homeserver) because olm_pk_decrypt has a stack-based buffer overflow. Remote code execution might be possible for some nonstandard build configurations.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2021-34813 is a libolm flaw where a malicious Matrix homeserver can crash a Matrix client during encrypted room key backup retrieval. The source notes remote code execution might be possible only in some nonstandard build configurations, so the confirmed impact is client crash.

Executive priority

Treat this as a targeted remediation item for Matrix environments. The confirmed business risk is client denial of service from a malicious homeserver; urgency increases if the organization uses custom or nonstandard libolm builds.

Technical view

Matrix libolm before 3.2.3 has a stack-based buffer overflow in olm_pk_decrypt when handling encrypted room key backup retrieval from a homeserver. The public record names client crash as the demonstrated outcome and flags possible RCE only for some nonstandard builds.

Likely exposure

Exposure is likely in Matrix clients or applications bundling libolm versions before 3.2.3, especially where clients retrieve encrypted room key backups from homeservers. The bundle does not identify specific downstream products or package inventories.

Exploitation context

The provided sources do not show active exploitation, and CVE-2021-34813 is not marked KEV. The described attacker position is a malicious Matrix homeserver interacting with a client during room key backup retrieval.

Researcher notes

Evidence is limited to the CVE description and Matrix references. Do not assume broad product exposure or proven RCE. Focus analysis on libolm version, olm_pk_decrypt usage, room key backup flows, and build hardening differences.

Mitigation direction

  • Upgrade libolm to 3.2.3 or later where used.
  • Check vendor guidance for Matrix clients bundling libolm.
  • Inventory applications that embed or statically link libolm.
  • Prioritize clients that connect to untrusted homeservers.
  • Review nonstandard build configurations for memory-safety exposure.

Validation and detection

  • Confirm deployed libolm versions are 3.2.3 or later.
  • Check Matrix client dependency manifests and bundled libraries.
  • Verify whether encrypted room key backup retrieval is enabled.
  • Review build flags against vendor guidance for RCE risk.
  • Confirm no unsupported fork remains on pre-3.2.3 code.
Prepared
Confidence
medium
Sources
5

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

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Execution behavior lookup

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CVE-2021-34813 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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