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CVE-2026-61911

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle....

4.3 MediumFix available

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
Low
Integrity
None
Availability
None

Exploit likelihood

0.22%Unchanged since Sep 10, 2026
90%50%10%1%

What each source reports

CVE List Score used 4.3

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Record
CVE-2026-61911
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness
CWE-497
Updated
2026-11-02
EUVDEUVD-2026-75129 4.3

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Record
EUVD-2026-75129
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-v69j-37vj-46wc 4.3

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle....

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Record
GHSA-v69j-37vj-46wc
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness
CWE-497
Updated
2026-11-02
NVD 4.3

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Record
CVE-2026-61911
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness
CWE-497
Updated
2026-11-02
OSV 4.3

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Record
CVE-2026-61911
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness
CWE-497
Updated
2026-11-02
OSVDEBIAN-CVE-2026-61911 4.3

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Record
DEBIAN-CVE-2026-61911
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Updated
2026-11-02
Show 4 moreShow less
OSVUBUNTU-CVE-2026-61911 4.3

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Record
UBUNTU-CVE-2026-61911
CVSS 3.1
4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Updated
2026-11-02
OSVCLSA-2026-1790173408 No score

cyrus-imapd: Fix of 3 CVEs

  • fix CVE-2026-61915: double-free in the CalDAV VPATCH BYPARAM selector
  • fix CVE-2026-61909: calendar/addressbook-multiget returned resources the user has no ACL on
  • fix CVE-2026-61911: Sieve mailboxexists/metadata probed other users' mailboxes without a lookup-rights check
  • do not free VPATCH parameters already removed by reference: libical frees them in icalproperty_remove_parameter_by_ref(), so the following icalparameter_free() aborted the CalDAV worker on any VPATCH carrying a PATCH-ACTION parameter, before the CVE-2026-61915 code path could be reached
  • add the upstream cunit regression test for CVE-2026-61915
  • run the cunit suite in %check even when cassandane is disabled, so the regression test above actually executes
Record
CLSA-2026-1790173408
Updated
2026-11-02
OSVCLSA-2026-1790974923 No score

cyrus-imapd: Fix of 2 CVEs

  • fix CVE-2026-61911: Sieve mailboxexists/metadata tests ignored the lookup ACL on another user's mailbox
  • fix CVE-2026-61909: CalDAV/CardDAV multiget did not check the ACL of each requested href
Record
CLSA-2026-1790974923
Updated
2026-11-02
OSVopenSUSE-SU-2026:21929-1 No score

Security update for cyrus-imapd

This update for cyrus-imapd fixes the following issues:

Changes in cyrus-imapd:

Update to 3.8.8 (bugfix release):

  • CVE-2026-61907: JMAP snooze bypasses destination-mailbox ACL (bsc#1279908)
  • CVE-2026-61908: JMAP email-header blob ID out-of-bounds index (bsc#1279975)
  • CVE-2026-61909: CalDAV/CardDAV multiget bypasses per-href ACL (bsc#1279976)
  • CVE-2026-61910: Mailbox/set let sharee change special-use role on shared mailboxes (bsc#1279977)
  • CVE-2026-61911: Sieve mailbox existence oracle (bsc#1279978)
  • CVE-2026-61915: VPATCH BYPARAM double-free (bsc#1279979)
Record
openSUSE-SU-2026:21929-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
cyrus-imapd
TuxCare:AlmaLinux:9.6
From an advisory covering 3 CVEs
 before 3.4.8-2.el9_6.tuxcare.els1
3.4.8-2.el9_6.tuxcare.els1
cyrus-imapd-devel
TuxCare:AlmaLinux:9.6
From an advisory covering 3 CVEs
 before 3.4.8-2.el9_6.tuxcare.els1
3.4.8-2.el9_6.tuxcare.els1
cyrus-imapd-doc-extra
TuxCare:AlmaLinux:9.6
From an advisory covering 3 CVEs
 before 3.4.8-2.el9_6.tuxcare.els1
3.4.8-2.el9_6.tuxcare.els1
cyrus-imapd-libs
TuxCare:AlmaLinux:9.6
From an advisory covering 3 CVEs
 before 3.4.8-2.el9_6.tuxcare.els1
3.4.8-2.el9_6.tuxcare.els1
cyrus-imapd-utils
TuxCare:AlmaLinux:9.6
From an advisory covering 3 CVEs
 before 3.4.8-2.el9_6.tuxcare.els1
3.4.8-2.el9_6.tuxcare.els1
cyrus-imapd-virusscan
TuxCare:AlmaLinux:9.6
From an advisory covering 3 CVEs
 before 3.4.8-2.el9_6.tuxcare.els1
3.4.8-2.el9_6.tuxcare.els1
perl-Cyrus
TuxCare:AlmaLinux:9.6
From an advisory covering 3 CVEs
 before 3.4.8-2.el9_6.tuxcare.els1
3.4.8-2.el9_6.tuxcare.els1
cyrus-imapd
TuxCare:AlmaLinux:9.2
From an advisory covering 2 CVEs
 before 3.4.1-7.el9_2.tuxcare.els3
3.4.1-7.el9_2.tuxcare.els3
cyrus-imapd-devel
TuxCare:AlmaLinux:9.2
From an advisory covering 2 CVEs
 before 3.4.1-7.el9_2.tuxcare.els3
3.4.1-7.el9_2.tuxcare.els3
cyrus-imapd-doc-extra
TuxCare:AlmaLinux:9.2
From an advisory covering 2 CVEs
 before 3.4.1-7.el9_2.tuxcare.els3
3.4.1-7.el9_2.tuxcare.els3
Show 14 moreShow less
Affected packages
PackageAffectedFixed
cyrus-imapd-libs
TuxCare:AlmaLinux:9.2
From an advisory covering 2 CVEs
 before 3.4.1-7.el9_2.tuxcare.els3
3.4.1-7.el9_2.tuxcare.els3
cyrus-imapd-utils
TuxCare:AlmaLinux:9.2
From an advisory covering 2 CVEs
 before 3.4.1-7.el9_2.tuxcare.els3
3.4.1-7.el9_2.tuxcare.els3
cyrus-imapd-virusscan
TuxCare:AlmaLinux:9.2
From an advisory covering 2 CVEs
 before 3.4.1-7.el9_2.tuxcare.els3
3.4.1-7.el9_2.tuxcare.els3
perl-Cyrus
TuxCare:AlmaLinux:9.2
From an advisory covering 2 CVEs
 before 3.4.1-7.el9_2.tuxcare.els3
3.4.1-7.el9_2.tuxcare.els3
cyrus-imapd
Debian:12
 All versions, plus listed versions
3.10.0-13.10.0~beta1-13.10.0~beta1-23.10.0~beta1-33.10.0~beta2-1
Show 40 moreShow less
3.10.0~rc2-13.10.1-13.10.1-23.10.1-33.10.1-3~bpo12+13.10.2-13.10.2-1~bpo12+13.12.0-13.12.0-23.12.1-13.12.1-23.12.1-33.12.2-13.12.3-13.12.3-1~bpo13+13.12.3-23.12.3-33.12.3-43.12.4-13.6.1-43.6.1-4+deb12u13.6.1-4+deb12u23.6.1-4+deb12u33.6.1-4+deb12u43.6.1-4+deb12u53.8.0-13.8.0-23.8.0-33.8.0-43.8.0-53.8.0~beta1-13.8.0~beta2-13.8.0~rc1-13.8.1-13.8.1-1~bpo12+13.8.1-23.8.1-33.8.2-13.8.3-13.8.4-1
 None known
cyrus-imapd
Debian:13
 All versions, plus listed versions
3.10.2-13.10.2-1+deb13u13.10.2-1+deb13u23.12.0-13.12.0-2
Show 10 moreShow less
3.12.1-13.12.1-23.12.1-33.12.2-13.12.3-13.12.3-1~bpo13+13.12.3-23.12.3-33.12.3-43.12.4-1
 None known
cyrus-imapd
Debian:14
 before 3.12.4-1, plus listed versions
3.10.2-13.12.0-13.12.0-23.12.1-13.12.1-2
Show 7 moreShow less
3.12.1-33.12.2-13.12.3-13.12.3-1~bpo13+13.12.3-23.12.3-33.12.3-4
3.12.4-1
cyrus-imapd
Ubuntu:Pro:18.04:LTS
 All versions, plus listed versions
2.5.10-3build12.5.10-3build22.5.10-3ubuntu12.5.10-3ubuntu1.12.5.10-3ubuntu1.1+esm1
 None known
cyrus-imapd
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
3.0.11-13.0.11-1build13.0.12-13.0.12-23.0.12-2ubuntu2
Show 7 moreShow less
3.0.12-2ubuntu33.0.13-2ubuntu13.0.13-3ubuntu13.0.13-4ubuntu13.0.13-53.0.13-5ubuntu0.1~esm13.0.13-5ubuntu0.1~esm2
 None known
cyrus-imapd
Ubuntu:Pro:22.04:LTS
 All versions, plus listed versions
3.2.6-2build13.4.2-23.4.2-2build13.4.3-23.4.3-3
Show 5 moreShow less
3.4.3-3build23.4.3-3ubuntu0.13.4.3-3ubuntu0.1+esm13.4.3-3ubuntu0.33.4.3-3ubuntu0.3+esm1
 None known
cyrus-imapd
Ubuntu:Pro:24.04:LTS
 All versions, plus listed versions
3.8.0-53.8.1-13.8.1-1build13.8.1-1build23.8.1-3
Show 5 moreShow less
3.8.1-3build33.8.2-13.8.2-1ubuntu0.1~esm13.8.2-1ubuntu0.23.8.2-1ubuntu0.2+esm1
 None known
cyrus-imapd
Ubuntu:26.10
 All versions, plus listed versions
3.12.1-33.12.2-13.12.2-1build13.12.3-3build1
 None known
cyrus-imapd
Ubuntu:26.04:LTS
 All versions, plus listed versions
3.10.2-13.12.1-23.12.1-2build13.12.1-3
 None known
cyrus-imapd
openSUSE:Leap 16.0
From an advisory covering 6 CVEs
 before 3.8.8-bp160.1.1
3.8.8-bp160.1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-61911 is a medium vulnerability (CVSS 4.3) in Cyrus Imap, published September 9, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.22%, the 12th percentile. Fixed in cyrus-imapd 3.12.4-1.

References

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