CVE-2021-44538Network attack vector

Remote memory corruption via session-description buffer overflow

Published Dec 14, 2021 · Updated Aug 4, 2024

Buffer overflow in Matrix libolm before 3.2.8 allows remote attackers to corrupt application memory through crafted encrypted messages. The olm_session_describe debugging function writes a partially attacker-controlled rendering of remotely influenced Olm session state past certain caller-provided buffers; overflow bytes are limited to ASCII spaces and digits, and safe sizes were undocumented. The path is reachable when matrix-js-sdk uses libolm for end-to-end encryption; Matrix reports remote triggering but considers successful exploitation impractical.

CVSS severity9.8
Critical
EPSS probability1.92%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Matrix libolm before 3.2.8 allows remote attackers to corrupt application memory through crafted encrypted messages. The olm_session_describe debugging function writes a partially attacker-controlled rendering of remotely influenced Olm session state past certain caller-provided buffers; overflow bytes are limited to ASCII spaces and digits, and safe sizes were undocumented. The path is reachable when matrix-js-sdk uses libolm for end-to-end encryption; Matrix reports remote triggering but considers successful exploitation impractical.

The record

CVE
CVE-2021-44538
Published
Dec 14, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-119, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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