An attacker that has valid credentials can select a compression algorithm for the IMAP connection whose decompression state requires a large amount of memory, and open several such connections. The memory limit of the process is reached with only a few connections, terminating the process and all connections it handles, which can cause degradation or denial of service for IMAP. Disable IMAP compression. Alternatively limit the number of connections handled by a single imap-login process, though this has a performance impact. Update to non-vulnerable version. No publicly available exploits are known.

The comparison used for the doveadm password and API key is not fully timing safe and can reveal the length of the configured secret. An attacker with access to the same network as the doveadm service, able to make repeated requests and measure response timing accurately, can learn the length of the secret, which reduces the effort needed to guess it. The secret value itself is not disclosed. Restrict network access to the doveadm service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

Forwarding information received from a host listed as a trusted proxy is not kept separate from Dovecot's own authentication fields, so a value sent by that host can be injected as an internal authentication field. Any host permitted to act as a trusted proxy can authenticate as any user without knowing that user's password. This affects deployments whose password database honours a field that permits authentication without a password. Deployments that do not configure trusted proxies are not affected. Restrict the list of trusted proxy networks to hosts that are fully under your control. Update to non-vulnerable version. No publicly available exploits are known.

An unauthenticated attacker can crash the ManageSieve login process by sending a small malformed command before authenticating. If running in high-security mode (default for community releases), only the attacker's own connection is terminated. If running in high-performance mode (default for Pro releases), all connections handled by the same managesieve-login process are terminated. Repeating the attack can cause denial of service for Sieve script management. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.

Attacker can use the IMAP SETACL command to inject the anyone permission to user's dovecot-acl file even if imapaclallowanyone=no. This causes folders to be spammed to all users. The impact is limited to being able to spam folders to other users, no unexpected access is gained. Install to fixed version. No publicly available exploits are known.

An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left open. In particular, the fix was for closing braces, but you could still use open braces to bypass the limit. Using excessive bracing, attacker can cause memory usage up to configured memory limit. Install fixed version, or configure vszlimit for imap process to low value. No publicly available exploits are known.

Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly available exploits are known.

Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel binding. This requires that the attacker is able to position itself between Dovecot and the client connection. If successful, the attacker can eavesdrop communications between Dovecot and client as MITM proxy. Install fixed version. No publicly available exploits are known.

Last updated 2 June 2026

Attacker can send a specifically crafted message before authentication that causes managesieve to allocate large amount of memory. Attacker can force managesieve-login to be unavailable by repeatedly crashing the process. Protect access to managesieve protocol, or install fixed version. No publicly available exploits are known.

Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Figuring out the credential will lead into full access to the affected component. Limit access to the doveadm http service port, install fixed version. No publicly available exploits are known.

A mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU. A suitably formatted mail message causes mail delivery process to consume large amounts of CPU time. Use MTA capabilities to limit RFC 2231 MIME parameters in mail messages, or upgrade to fixed version where the processing is limited. No publicly available exploits are known.

If authusernamechars is empty, it is possible to inject arbitrary LDAP filter to Dovecot's LDAP authentication. This leads to potentially bypassing restrictions and allows probing of LDAP structure. Do not clear out authusernamechars, or install fixed version. No publicly available exploits are known.

Attacker can send a specifically crafted message before authentication that causes managesieve to allocate large amount of memory. Attacker can force managesieve-login to be unavailable by repeatedly crashing the process. Protect access to managesieve protocol, or install fixed version. No publicly available exploits are known.

Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Install fixed version, there is no other remediation. No publicly available exploits are known.

Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Figuring out the credential will lead into full access to the affected component. Limit access to the doveadm http service port, install fixed version. No publicly available exploits are known.

Dovecot SQL based authentication can be bypassed when authusernamechars is cleared by admin. This vulnerability allows bypassing authentication for any user and user enumeration. Do not clear authusernamechars. If this is not possible, install latest fixed version. No publicly available exploits are known.

Dovecot OTP authentication is vulnerable to replay attack under specific conditions. If auth cache is enabled, and username is altered in passdb, then OTP credentials can be cached so that same OTP reply is valid. An attacker able to observe an OTP exchange is able to log in as the user. If authentication happens over unsecure connection, switch to SCRAM protocol. Alternatively ensure the communcations are secured, and if possible switch to OAUTH2 or SCRAM. No publicly available exploits are known.

When dovecot has been configured to use per-domain passwd files, and they are placed one path component above /etc, or slash has been added to allowed characters, path traversal can happen if the domain component is directory partial. This allows inadvertently reading /etc/passwd (or some other path which ends with passwd). If this file contains passwords, it can be used to authenticate wrongly, or if this is userdb, it can unexpectly make system users appear valid users. Upgrade to fixed version, or use different authentication scheme that does not rely on paths. Alternatively you can also ensure that the per-domain passwd files are in some other location, such as /etc/dovecot/auth/%d. No publicly available exploits are known.

ManageSieve AUTHENTICATE command crashes when using literal as SASL initial response. This can be used to crash ManageSieve service repeatedly, making it unavailable for other users. Control access to ManageSieve port, or disable the service if it's not needed. Alternatively upgrade to a fixed version. No publicly available exploits are known.

Dovecot has provided a script to use for attachment to text conversion. This script unsafely handles zip-style attachments. Attacker can use specially crafted OOXML documents to cause unintended files on the system to be indexed and subsequently ending up in FTS indexes. Do not use the provided script, instead, use something else like FTS tika. No publicly available exploits are known.

When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all active authentication sessions to fail. Invalid BASE64 data can be used to DoS a vulnerable server to break concurrent logins. Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments). No publicly available exploits are known.

When cache is enabled, some passdb/userdb drivers incorrectly cache all users with same cache key, causing wrong cached information to be used for these users. After cached login, all subsequent logins are for same user. Install fixed version or disable caching either globally or for the impacted passdb/userdb drivers. No publicly available exploits are known.

-------- Original Message -------- From: Aki Tuomi via Dovecot-news <dovecot-news () dovecot org> Sent: October 29, 2025 8:22:46 AM UTC To: "dovecot () dovecot org" <dovecot () dovecot org>, "dovecot-news () dovecot org" <dovecot-news () dovecot org> Subject: [Dovecot-news] CVE-2025-30189 notification

Affected product: Dovecot IMAP Server Internal reference: DOV-7830 Vulnerability type: CWE-1250 (Improper Preservation of Consistency Between Independent Representations of Shared State) Vulnerable version: 2.4.0, 2.4.1 Vulnerable component: auth Report confidence: Confirmed Solution status: Fixed in 2.4.2 Researcher credits: Erik <erik () broadlux com> Vendor notification: 2025-07-25 CVE reference: CVE-2025-30189 CVSS: 7.4 (CVSS3.1:AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N)

Vulnerability Details: Using auth caching with oauth2 passdb, passwd passdb or userdb, or passwd userdb, causes the first lookup to be cached for all the lookups. This is because the cache key is "%u" which no longer actually expands to same as "%{user}".

Workaround: Disabling auth cache will prevent the issue.

Fix Install non-vulnerable version of Dovecot. Patch can be found at https://github.com/dovecot/core/compare/a70ce7d3e2f983979e971414c5892c4e30197231%5E...34caed79b76a7b82a2a9c94cf35371bec6c2b826.patch

Dovecot accepts dot LF DOT LF symbol as end of DATA command. RFC requires that it should always be CR LF DOT CR LF. This causes Dovecot to convert single mail with LF DOT LF in middle, into two emails when relaying to SMTP. Dovecot will split mail with LF DOT LF into two mails. Upgrade to latest released version. No publicly available exploits are known.

Vulnerability Details: Very large headers can cause resource exhaustion when parsing message. The message-parser normally reads reasonably sized chunks of the message. However, when it feeds them to message-header-parser, it starts building up "fullvalue" buffer out of the smaller chunks. The fullvalue buffer has no size limit, so large headers can cause large memory usage. It doesn't matter whether it's a single long header line, or a single header split into multiple lines. This bug exists in all Dovecot versions.

Incoming mails typically have some size limits set by MTA, so even largest possible header size may still fit into Dovecot's vszlimit. So attackers probably can't DoS a victim user this way. A user could APPEND larger mails though, allowing them to DoS themselves (although maybe cause some memory issues for the backend in general).

Workaround: One can implement restrictions on headers on MTA component preceding Dovecot.

Fix: Install non-vulnerable version of Dovecot. Patch can be found at https://github.com/dovecot/core/compare/f020e13%5E...ce88c33.patch

Vulnerability Details: Having a large number of address headers (From, To, Cc, Bcc, etc.) becomes excessively CPU intensive. With 100k header lines CPU usage is already 12 seconds, and in a production environment we observed 500k header lines taking 18 minutes to parse. Since this can be triggered by external actors sending emails to a victim, this is a security issue.

The main problem is that each header line's address is added to the end of a linked list. This is done by walking the whole linked list, which becomes more inefficient the more addresses there are.

Workaround: One can implement restrictions on address headers on MTA component preceding Dovecot.

Fix: Install non-vulnerable version of Dovecot. Patch can be found at https://github.com/dovecot/core/compare/8e4c42d%5E...1481c04.patch

Affected product: Dovecot IMAP Server Internal reference: DOV-6601 Vulnerability type: CWE-770 (Allocation of Resources Without Limits or Throttling) Vulnerable version: 2.2, 2.3 Vulnerable component: lib-mail Report confidence: Confirmed Solution status: Fixed in 2.3.21.1 Researcher credits: Vendor internal discovery Vendor notification: 2024-01-31 CVE reference: CVE-2024-23185 CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Vulnerability Details: Very large headers can cause resource exhaustion when parsing message. The message-parser normally reads reasonably sized chunks of the message. However, when it feeds them to message-header-parser, it starts building up "fullvalue" buffer out of the smaller chunks. The fullvalue buffer has no size limit, so large headers can cause large memory usage. It doesn't matter whether it's a single long header line, or a single header split into multiple lines. This bug exists in all Dovecot versions.

Incoming mails typically have some size limits set by MTA, so even largest possible header size may still fit into Dovecot's vszlimit. So attackers probably can't DoS a victim user this way. A user could APPEND larger mails though, allowing them to DoS themselves (although maybe cause some memory issues for the backend in general).

Workaround: One can implement restrictions on headers on MTA component preceding Dovecot.

Fix: Install non-vulnerable version of Dovecot. Patch can be found at https://github.com/dovecot/core/compare/f020e13%5E...ce88c33.patch

Affected product: Dovecot IMAP Server Internal reference: DOV-6464 Vulnerability type: CWE-770 (Allocation of Resources Without Limits or Throttling) Vulnerable version: 2.2, 2.3 Vulnerable component: lib-mail Report confidence: Confirmed Solution status: Fixed in 2.3.21.1 Researcher credits: Vendor internal discovery Vendor notification: 2024-01-30 CVE reference: CVE-2024-23184 CVSS: 5.0 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N)

Vulnerability Details: Having a large number of address headers (From, To, Cc, Bcc, etc.) becomes excessively CPU intensive. With 100k header lines CPU usage is already 12 seconds, and in a production environment we observed 500k header lines taking 18 minutes to parse. Since this can be triggered by external actors sending emails to a victim, this is a security issue.

The main problem is that each header line's address is added to the end of a linked list. This is done by walking the whole linked list, which becomes more inefficient the more addresses there are.

Workaround: One can implement restrictions on address headers on MTA component preceding Dovecot.

Fix: Install non-vulnerable version of Dovecot. Patch can be found at https://github.com/dovecot/core/compare/8e4c42d%5E...1481c04.patch