olm, thunderbird — security advisory
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.
- Products
- olm, thunderbird
- Affected versions
- Not specified
- Fixed versions
- 1:91.4.1-1, 3.2.8~dfsg-1
- CVEs
- CVE-2021-44538
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 02:02 UTC · Revision 1
Source evidence
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.
osv:DEBIAN-CVE-2021-44538
olm
Fixed versions: 3.2.8~dfsg-1
olm
Fixed versions: 3.2.8~dfsg-1
olm
Fixed versions: 3.2.8~dfsg-1
thunderbird
Fixed versions: 1:91.4.1-1
thunderbird
Fixed versions: 1:91.4.1-1
thunderbird
Fixed versions: 1:91.4.1-1
Complete source record
{
"id": "8fc59015ddd2f6be309c8f6489a30d94019a93339966cb387590362556daf013",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2021-44538",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2021-44538",
"summary": "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.",
"evidence": "osv:DEBIAN-CVE-2021-44538",
"products": [
{
"name": {
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"evidence": "/affected/0/package/name"
},
"prerequisites": [],
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"evidence": "/affected/0/ranges"
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{
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{
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{
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{
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}
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"affected_versions": []
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{
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"affected_versions": []
}
],
"severity": "critical",
"structured": {
"id": "DEBIAN-CVE-2021-44538",
"aliases": [
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],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
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"type": "ECOSYSTEM",
"events": [
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{
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"package": {
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"ecosystem": "Debian:12"
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"database_specific": {
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"ecosystem_specific": {
"urgency": "not yet assigned"
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{
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{
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"package": {
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"ecosystem": "Debian:13"
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"database_specific": {
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"database_specific": {
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"package": {
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"ecosystem": "Debian:12"
},
"database_specific": {
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},
"ecosystem_specific": {
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}
},
{
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],
"package": {
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"purl": "pkg:deb/debian/thunderbird?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-44538.json"
},
"ecosystem_specific": {
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}
},
{
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],
"package": {
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"purl": "pkg:deb/debian/thunderbird?arch=source&distro=forky",
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},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-44538.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-23T18:05:23.574479928Z",
"provider": "osv",
"upstream": [
"CVE-2021-44538"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2021-44538"
]
},
"related_cves": [
{
"value": "CVE-2021-44538",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 424424,
"published_at": "2021-12-14T14:15:09.41+00:00"
}