High
varnish — security advisory
Varnish Cache 9 before 9.0.1 allows a "workspace overflow" denial of service (daemon panic) after timeout_linger. A malicious client could send an HTTP/1 request, wait long enough until the session releases its worker thread (timeout_linger) and resume traffic before the session is closed (timeout_idle) sending more than one request at once to trigger a pipelining operation between requests. This vulnerability affecting Varnish Cache 9.0.0 emerged from a port of the Varnish Enterprise non-blocking architecture for HTTP/2. New code was needed to adapt to a more recent workspace API that formalizes the pipelining operation. In addition to the workspace change on the Varnish Cache side, other differences created merge conflicts, like partial support for trailers in Varnish Enterprise. The conflict resolution missed one code path configuring pipelining to perform a complete workspace rollback, losing the guarantee that prefetched data would fit inside workspace_client during the transition from one request to the next. This can result in a workspace overflow, triggering a panic and crashing the Varnish server.
- Products
- varnish
- Affected versions
- 3.0.4-1ubuntu1, 3.0.4-1ubuntu2, 3.0.5-1ubuntu2, 3.0.5-2, 3.0.5-2ubuntu0.1, 4.0.3-1, 4.1.0-1, 4.1.0-2, 4.1.1-1, 4.1.1-1ubuntu0.2, 4.1.1-1ubuntu0.2+esm1, 5.0.0-7.1, 5.2.1-1, 5.2.1-1ubuntu0.1, 5.2.1-1ubuntu0.1+esm1, 6.1.1-1, 6.2.1-2, 6.2.1-2ubuntu0.1, 6.2.1-2ubuntu0.1~esm1, 6.2.1-2ubuntu0.1~esm2, 6.2.1-2ubuntu0.2, 6.2.1-2ubuntu0.2+esm1, 6.5.2-1, 6.6.1-1, 6.6.1-1ubuntu0.2, 6.6.1-1ubuntu0.2+esm1, 7.1.1-1.1ubuntu1, 7.7.0-1, 7.7.0-2, 7.7.0-3, 7.7.3-1, 7.7.3-1build1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-40396
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:43 UTC · Revision 1
Source evidence
Varnish Cache 9 before 9.0.1 allows a "workspace overflow" denial of service (daemon panic) after timeout_linger. A malicious client could send an HTTP/1 request, wait long enough until the session releases its worker thread (timeout_linger) and resume traffic before the session is closed (timeout_idle) sending more than one request at once to trigger a pipelining operation between requests. This vulnerability affecting Varnish Cache 9.0.0 emerged from a port of the Varnish Enterprise non-blocking architecture for HTTP/2. New code was needed to adapt to a more recent workspace API that formalizes the pipelining operation. In addition to the workspace change on the Varnish Cache side, other differences created merge conflicts, like partial support for trailers in Varnish Enterprise. The conflict resolution missed one code path configuring pipelining to perform a complete workspace rollback, losing the guarantee that prefetched data would fit inside workspace_client during the transition from one request to the next. This can result in a workspace overflow, triggering a panic and crashing the Varnish server.
osv:UBUNTU-CVE-2026-40396
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
varnish
Fixed versions: Not specified
Complete source record
{
"id": "fdd97549a33521fcd35bb4861fe600b0ce93c0833d03d9ee04c21397d0333391",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-40396",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-40396",
"summary": "Varnish Cache 9 before 9.0.1 allows a \"workspace overflow\" denial of service (daemon panic) after timeout_linger. A malicious client could send an HTTP/1 request, wait long enough until the session releases its worker thread (timeout_linger) and resume traffic before the session is closed (timeout_idle) sending more than one request at once to trigger a pipelining operation between requests. This vulnerability affecting Varnish Cache 9.0.0 emerged from a port of the Varnish Enterprise non-blocking architecture for HTTP/2. New code was needed to adapt to a more recent workspace API that formalizes the pipelining operation. In addition to the workspace change on the Varnish Cache side, other differences created merge conflicts, like partial support for trailers in Varnish Enterprise. The conflict resolution missed one code path configuring pipelining to perform a complete workspace rollback, losing the guarantee that prefetched data would fit inside workspace_client during the transition from one request to the next. This can result in a workspace overflow, triggering a panic and crashing the Varnish server.",
"evidence": "osv:UBUNTU-CVE-2026-40396",
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{
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{
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{
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{
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{
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{
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"evidence": "/affected/8/versions"
},
{
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],
"severity": "high",
"structured": {
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"aliases": [
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"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L"
},
{
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"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
},
{
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"package": {
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},
"versions": [
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},
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},
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}
],
"modified": "2026-10-17T12:58:53.276343272Z",
"provider": "osv",
"upstream": [
"CVE-2026-40396"
],
"references": [
"https://ubuntu.com/security/CVE-2026-40396",
"https://www.cve.org/CVERecord?id=CVE-2026-40396",
"https://github.com/varnish/varnish/issues/15",
"https://github.com/varnish/varnish/releases/tag/varnish-9.0.1",
"https://docs.varnish-software.com/security/VEV00002/"
]
},
"related_cves": [
{
"value": "CVE-2026-40396",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/1/score"
},
"source_id": "core-osv",
"document_id": 359135,
"published_at": "2026-04-12T20:16:00+00:00"
}