HOMEVULNERABILITIESCVE-2021-34813
CRITICAL

CVE-2021-34813

CWE-787Published: June 16, 2021· Updated: Jun 17, 2026

9.8
CVSS v3.1

Official Description

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.

NVD Source

Technical Analysis

CVE-2021-34813 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

From a weakness classification perspective (CWE-787): Out-of-bounds write vulnerabilities can lead to data corruption, crashes, or arbitrary code execution.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

matrix1 product(s)
olm
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901b
PATCHhttps://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolm
PATCHhttps://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901b
PATCHhttps://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolm
ADVISORYhttps://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3
ADVISORYhttps://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3

All References (6)

→
https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901bPatch · Vendor Advisory
→
https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3Release Notes · Vendor Advisory
→
https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolmExploit · Patch · Vendor Advisory
→
https://gitlab.matrix.org/matrix-org/olm/-/commit/ccc0d122ee1b4d5e5ca4ec1432086be17d5f901bPatch · Vendor Advisory
→
https://gitlab.matrix.org/matrix-org/olm/-/releases/3.2.3Release Notes · Vendor Advisory
→
https://matrix.org/blog/2021/06/14/adventures-in-fuzzing-libolmExploit · Patch · Vendor Advisory

Quick Facts

CVE IDCVE-2021-34813
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-787
CISA KEVNo
Affected1 vendor(s)
PublishedJun 16, 2021

Related CVEs (CWE-787)

CVE-2004-0574
10.0
CVE-2026-42369
10.0
CVE-2015-0235
10.0
CVE-2004-1287
10.0
CVE-2018-10718
10.0
CVE-2026-4746
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-34813 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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