CVE-2021-44538: The olm_session_describe function in Matrix libolm before 3.2.7 is vulnerable to a buffer overflow.
Noroxi assessment
Priority: Plan (action score 40/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 1.9% (FIRST EPSS); higher than 80.4% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- Fixed version: olm (Debian:12) 3.2.8~dfsg-1; thunderbird (Debian:12) 1:91.4.1-1; MozillaThunderbird (openSUSE:Leap 15.3) 91.4.1-8.48.1.
Add it to your regular patch cycle. Upgrade to olm (Debian:12) 3.2.8~dfsg-1; thunderbird (Debian:12) 1:91.4.1-1; MozillaThunderbird (openSUSE:Leap 15.3) 91.4.1-8.48.1 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
The olm_session_describe function in Matrix libolm before 3.2.7 is vulnerable to a buffer overflow. The Olm session object represents a cryptographic channel between two parties. Therefore, its state is partially controllable by the remote party of the channel. Attackers can construct a crafted sequence of messages to manipulate the state of the receiver's session in such a way that, for some buffer sizes, a buffer overflow happens on a call to olm_session_describe. Furthermore, safe buffer sizes were undocumented. The overflow content is partially controllable by the attacker and limited to ASCII spaces and digits. The known affected products are Element Web And SchildiChat Web.
- Published
- Dec 14, 2021
- Updated
- Jun 17, 2026
- EPSS
- 1.9% · 80th percentile
- CWE
- CWE-119
Report tools
Action score
40
Plan
Add it to your regular patch cycle.
- CVSS
- 39 / 40 · 9.8 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 1 / 30 · 1.9%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
Running WordPress? Scan your site free with WP Lens
Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| matrix | element | cpe:2.3:a:matrix:element |
| matrix | javascript sdk | cpe:2.3:a:matrix:javascript_sdk |
| matrix | olm | cpe:2.3:a:matrix:olm |
| schildi | schildichat | cpe:2.3:a:schildi:schildichat |
| cinny project | cinny | cpe:2.3:a:cinny_project:cinny |
| debian | debian linux | cpe:2.3:o:debian:debian_linux |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- cinny project cinnybefore 1.6.0
- debian debian linux10.0
- debian debian linux11.0
- debian debian linux9.0
- matrix elementbefore 1.9.7
- matrix javascript sdk2.4.2 and later · before 15.2.1
- matrix olm3.1.4 and later · before 3.2.8
- schildi schildichatbefore 1.9.7-sc1
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:12 | olm | before 3.2.8~dfsg-1 | 3.2.8~dfsg-1 |
| Debian:12 | thunderbird | before 1:91.4.1-1 | 1:91.4.1-1 |
| openSUSE:Leap 15.3 | MozillaThunderbird | before 91.4.1-8.48.1 | 91.4.1-8.48.1 |
| openSUSE:Leap 15.3 | zabbix | before 4.0.38-bp153.2.3.1 | 4.0.38-bp153.2.3.1 |
| openSUSE:Tumbleweed | MozillaThunderbird | before 91.4.1-1.1 | 91.4.1-1.1 |
| SUSE:Linux Enterprise Workstation Extension 15 SP3 | MozillaThunderbird | before 91.4.1-8.48.1 | 91.4.1-8.48.1 |
| SUSE:Package Hub 15 SP3 | zabbix | before 4.0.38-bp153.2.3.1 | 4.0.38-bp153.2.3.1 |
Same product
matrix: all recordsOther highest-scoring records for the same primary product.
- CVE-2021-40824A logic error in the room key sharing functionality of Element Android before 1.2.2 and matrix-android-sdk2 (aka Matrix SDK for Android) bef23Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| debian:olm | 3.2.8~dfsg-1 · Debian:12 | Package registry (OSV) |
| debian:thunderbird | 1:91.4.1-1 · Debian:12 | Package registry (OSV) |
| opensuse:MozillaThunderbird | 91.4.1-8.48.1 · openSUSE:Leap 15.3 | Package registry (OSV) |
| opensuse:zabbix | 4.0.38-bp153.2.3.1 · openSUSE:Leap 15.3 | Package registry (OSV) |
| suse:MozillaThunderbird | 91.4.1-8.48.1 · SUSE:Linux Enterprise Workstation Extension 15 SP3 | Package registry (OSV) |
| suse:zabbix | 4.0.38-bp153.2.3.1 · SUSE:Package Hub 15 SP3 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
CWE-119 · Improper Restriction of Operations within the Bounds of a Memory BufferCVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- Buffer Overflow via Environment VariablesCAPEC-10likelihood: High · High
- Overflow BuffersCAPEC-100likelihood: High · Very High
- Buffer ManipulationCAPEC-123likelihood: High · Very High
- Client-side Injection-induced Buffer OverflowCAPEC-14likelihood: Medium · High
- Filter Failure through Buffer OverflowCAPEC-24likelihood: High · High
- MIME ConversionCAPEC-42likelihood: High · High
- Overflow Binary Resource FileCAPEC-44likelihood: High · Very High
- Buffer Overflow via Symbolic LinksCAPEC-45likelihood: High · High
ATT&CK techniques
—
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (3 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.