2026-10-25 Release of logback version 1.6.6

• LoggingEventVO now rejects, during deserialization, throwable proxies whose cause or suppressed entries point back into the graph of proxies, for example to their own parent. Such graphs cannot be produced by logback itself. However, a crafted stream sent to a socket receiver could use serialization back-references to build them, after which DefaultThrowableRenderer and SyslogAppender would loop forever and the recursive converters would overflow the stack. These streams are now rejected with an InvalidObjectException. Circular exceptions logged by the application are still transmitted correctly. This issue was reported and fixed in PR #1079 by arfa-21.

• FileNamePattern now escapes characters with a special meaning in regular expressions, such as (, [ or +, when converting the literal parts of a file name pattern into a regex. Previously, RollingFileAppender failed to start when the path contained an unbalanced parenthesis, as in C:/Users/Michael(Financ. This issue was reported in issues/914 by danamlund. Moreover, with SizeAndTimeBasedRollingPolicy and a pattern such as app.%d.(%i).log, existing archives were not recognized. After a restart within the same period, the next rollover could overwrite an existing archive, and maxHistory and totalSizeCap never removed such archives. This issue was reported in issues/933 by GeoffreyBoulay. The fix was contributed in PR #1077 by Jialin Chen. Regex metacharacters in %d{...} date patterns are now escaped as well.

• The conversion of date patterns into regular expressions now follows the rules of DateTimeFormatter, which logback uses to format dates, instead of those of SimpleDateFormat. In particular, the L (stand-alone month) pattern letter is now supported.

• SyslogOutputStream now connects its DatagramSocket to the syslog host. Previously, the socket was bound to the wildcard address, so that hardened environments saw an unconnected UDP listener on all interfaces for as long as the application ran. This issue was reported in issues/939 by joao-rebelo. The fix was contributed in PR #1076 by Lyin-OTTF.

If the socket cannot be connected, for example because the network is not yet available, SyslogOutputStream falls back to an unconnected socket and SyslogAppenderBase emits a warning. When a datagram sent on a connected socket fails due to an ICMP "port unreachable" message caused by an earlier datagram, the datagram is sent once more so that no message is lost. If the retry also fails, a single warning is emitted instead of one error per event.

• OutputStreamAppender now stops its encoder when the appender is stopped. Previously, encoders holding resources until they were stopped, such as those of logstash-logback-encoder, were never released, causing heap growth at each reconfiguration. This issue was fixed in PR #1072 by Samuel Fernandes.

• During variable substitution, an unmatched right curly brace now causes an error to be reported, with the original value left unchanged. Previously, the brace and all subsequent characters were silently dropped, so that %m}some text became %m. This issue was reported in issues/836 by philsttr.

• LogbackMDCAdapter now stores MDC entries in a LinkedHashMap, so that the %X converter outputs them in insertion order. This issue was reported in LOGBACK-1337 and fixed by Craig P. Motlin.

• A bit-wise identical binary of this version can be reproduced by building from source code at commit a9ee801 associated with the tag v_1.6.6. The release was built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

2026-09-30 Release of logback version 1.6.5

• Fixed a vulnerability CVE-2026-104721 closely related to CVE-2026-19880. The fix in version 1.6.3, which strips forward and backward slashes from MDC values, was insufficient. An MDC value could still contain relative path components such as .., variable references such as /, or characters that are special in file name patterns and email addresses. This latest vulnerability was found and reported by François Martin (GitHub: @martinfrancois, https://github.com/martinfrancois).

MDCBasedDiscriminator, used by SiftingAppender, now rejects MDC values instead of stripping characters from them. An MDC value is rejected if it is empty, if it is longer than 64 characters, if it contains the sequence .., or if it contains any of the following characters: / \ $ { } [ ] ( ) | ? * + % , @. When an MDC value is rejected, the discriminator returns the value of its DefaultValue property. A warning is emitted for each rejected value. These warnings are rate-limited.

• When compression is enabled, TimeBasedRollingPolicy and SizeAndTimeBasedRollingPolicy now also remove old log files that were never compressed, for example because the application was not running at rollover time. Previously, such files were ignored by maxHistory and accumulated indefinitely. This issue was discussed in discussions/1032. See TimeBasedRollingPolicy.

• SimpleInvocationGate, deprecated in version 1.6.3, is now marked for removal. Use FixedIntervalInvocationGate instead.

• A bit-wise identical binary of this version can be reproduced by building from source code at commit d1b829d associated with the tag v_1.6.5. The release was built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

2026-09-24 Release of logback version 1.6.4

• Variable substitution is again applied to the scan attribute of the <configuration> element. The scanning refactoring in version 1.5.27 had dropped substitution, so values such as ${logback.scan.enabled:-true} were no longer resolved. As before version 1.5.27, an unrecognized non-empty value turns scanning on. The same substitution now applies to the scan attribute of <propertiesConfigurator>. This regression was reported in issues/1065 by vaibhavjain2.

• OutputStreamAppender and FileAppender now handle stateful encoders. The Encoder interface has a new default method called isStateful(), which returns false. An encoder that keeps state between calls to encode() can return true. For such encoders, the appender holds its write lock while encoding and while writing, so the output of concurrent appends cannot interleave. Stateless encoders still encode outside the lock, so their performance does not change. Existing encoders need no changes.

• Several race conditions in OutputStreamAppender and FileAppender were fixed. The appender is now marked started and the encoder header is written while the same lock is held, so a concurrent append can no longer write an event before the header. After acquiring the lock, the appender checks again whether it has been stopped, so no event is written after the footer. In prudent mode, FileAppender now encodes and writes each event while holding the lock.

• Fixed a data race on the logger count in LoggerContext. Loggers are created under the lock of their parent logger, so loggers with different parents could be created at the same time and increments of the shared counter could be lost. As a result, LoggerContext.size() could return a value lower than the actual number of loggers. The counter is now an AtomicInteger. This issue was reported in issues/1038 by hcantunc. The fix was contributed in PR #1055 by seonwoo_jung.

• TimeBasedRollingPolicy now supports half-day periods. Date patterns with the AM/PM marker, for example %d{yyyy-MM-dd-a}, used to be detected as daily and rolled over only at midnight. They now roll over at both 00:00 and 12:00. This issue was reported in issues/976 by shakthifuture. The fix was contributed in PR #1051 by seonwoo_jung. See TimeBasedRollingPolicy.

• If org.jline.jansi.AnsiConsole cannot be found on the class path, JansiConsoleAppender now emits warnings that explain how to add org.jline:jansi-core and then writes to the plain console stream. See codes.html#missingJlineJansi.

• The unused ch.qos.logback.classic.util.LogbackMDCAdapterSimple class was removed. LogbackMDCAdapter remains the default MDC adapter.

• A bit-wise identical binary of this version can be reproduced by building from source code at commit 07d291c associated with the tag v_1.6.4. The release was built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

Full Changelog: v_1.6.3...v_1.6.4

2026-08-14 Release of logback version 1.6.3

• In response CVE-2026-19880, MDCBasedDiscriminator (used by SiftingAppender) now strips forward and backward slashes (/, \) from MDC values before they are used as discriminating keys. This prevents path segments from escaping into destinations controlled by an attacker. When sanitisation actually changes a value, a warning is emitted; the warning is rate-limited (a small batch, then a lull of about ten minutes).

• Colour console support is split out into a dedicated JansiConsoleAppender. It wraps stdout or stderr with Jansi so ANSI escape sequences (for example coloured patterns) render correctly on terminals that need it, notably Windows. Prefer this class over the older path described next. See the appenders documentation.

• The withJansi property on ConsoleAppender is deprecated. Existing configurations that still set <withJansi>true</withJansi> continue to work for compatibility, but new setups should use JansiConsoleAppender instead.

• ConsoleAppender no longer treats the process console as an exclusive resource: stopping it does not close System.out / System.err. JansiConsoleAppender pairs each AnsiConsole.systemInstall() with systemUninstall() on stop, so repeated start/stop cycles do not leave Jansi installed or tear down streams shared with the rest of the JVM. Related behavior is covered by tests for issues/1063.

• Invocation throttling helpers were reworked: SimpleInvocationGate is renamed FixedIntervalInvocationGate, and BatchedFixedIntervalInvocationGate allows a short burst of invocations before applying a fixed lull. The sanitisation
  warning above uses the batched gate.

• The JPMS module-info for logback-core now exports the ch.qos.logback.core.property package, which had been missing from the module descriptor.

• A bit-wise identical binary of this version can be reproduced by building from source code at commit e8e824dede022a6d7208b36cfa875b0d1b7772f3 associated with the tag v_1.6.3. The release was built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

--
Sponsoring SLF4J/logback/reload4j at https://github.com/sponsors/qos-ch

2026-08-10 Release of logback version 1.6.2

• Configuration analysis now detects contradictory caller-data inclusion instructions. For example, an AsyncAppender, SocketAppender or SMTPAppender with includeCallerData left at the default false is incompatible with a layout or encoder pattern that uses a caller-data converter such as %C, %M, %L, %F, %l or %caller. At runtime those converters would print question marks and still incur extraction cost on a worker thread. Logback now emits a configuration-time warning when such instructions disagree. See codes.html#callerContradiction for details. This issue was reported in issues/1059 by leeychee. The initial analysis was contributed by seonwoo_jung.

• Caller-contradiction analysis can be turned off by setting the logback.skipCallerContradictionAnalysis variable to true, either as a system property (-Dlogback.skipCallerContradictionAnalysis=true) or as a property in the configuration file:

  <property name="logback.skipCallerContradictionAnalysis" value="true"/>

• SimpleSocketServer and SimpleSSLSocketServer now require an explicit client IP whitelist. On the command line, pass one or more allowed addresses (single IPs or CIDR ranges) after the configuration file. An empty whitelist means no clients are accepted. When embedding the server programmatically, register allowed addresses with addAllowedClientAddress(String) or setAllowedClientAddresses(Collection) before clients connect. See the documentation on restricting client access.

• Added ThrowableProxyVOBuilder for assembling a ThrowableProxyVO field by field, with a corresponding ThrowableProxyVO.builder() entry point.

• Dependency analysis handlers now run their postHandle method after child models have been processed, so checks that depend on nested appenders (such as caller-contradiction analysis) see a complete picture.

• Updated several dependencies, including Angus Mail to 2.0.4 and Jetty (test) to 12.1.12.

• A bit-wise identical binary of this version can be reproduced by building from source code at commit e3d7833 associated with the tag v_1.6.2. The release was built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

2026-07-28 Release of logback version 1.6.1

• In TimeBasedRollingPolicy, when the file option is set, the intermediate file renamed before asynchronous compression now receives the target archive name without the compression suffix (e.g. .gz, .zip, .xz). Previously it used a nanotime-based .tmp suffix. This makes the file easier to identify if compression fails during rollover. (See also the following paragraph.)

• On GZ, ZIP, or XZ compression failure, the original (uncompressed) log file is no longer deleted. Compression strategies now delete the source file only after successful compression and emit a warning that the original was left intact.

• ConsoleAppender with now probes JLine's org.jline.jansi.AnsiConsole first and falls back to the legacy FuseSource org.fusesource.jansi.AnsiConsole class. This keeps ANSI coloring working after Jansi moved under the JLine project. The optional org.jline:jansi-core artifact is declared as a dependency alongside the existing FuseSource jansi dependency. A preferredJansiClassName property was added for tests. This issue was reported in issues/1043 by seonwoo_jung who also provided the relevant PR.

• LayoutWrappingEncoder now reports an error at start() when no layout is set and guards encode() against a null layout. Previously, a missing layout (for example after an ignored // branch) allowed the encoder to start and then fail with a NullPointerException on every event, resulting in silent log loss. This issue was reported in issues/1046 by seonwoo_jung who also provided the relevant PR.

• FileCollisionAnalyser now detects file collisions involving nested appenders of SiftingAppender. When the nested file or fileNamePattern does not textually reference the discriminator key (e.g. ${userId}), a warning is issued at configuration time naming the appender, the key, and the shared target. This closes a gap where statically declared file appenders were checked but sifted nested appenders were not. This enhancement was contributed in PR #1041 by seonwoo_jung.

• More defensive handling in SyslogOutputStream and SyslogAppenderBase: the close() method now ensures that resources are closed, writes and flushes check that the underlying resources are in a valid state and fallback to no-op otherwise.

• A bit-wise identical binary of this version can be reproduced by building from source code at commit 57759f4 associated with the tag v_1.6.1. The release was built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

• See https://logback.qos.ch/news.html#1.6.1 for the original text.

2026-07-23 Release of logback version 1.6.0

• Removed certain deprecated variables, methods, and classes. For the list of removed members see release_1.6.0.txt.

• In AsyncAppenderBase, the put(ILoggingEvent) method now has the protected modifier to allow access from derived classes. This change was requested by Thomas Skjølberg in pr#1053.

• Bump SLF4J dependency to version 2.0.18.

• See also the overview of the 1.6.x series.

• A bit-wise identical binary of this version can be reproduced by building from source code at commit b07adf3 associated with the tag v_1.6.0. The release was built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

2026-07-09 Release of logback version 1.5.38

• In HardenedObjectInputStream, fixed a typo preventing Throwable objects from being white-filtered. This issue was reported in PR #1045 by t0rchwo0d.

• A bitwise identical binary of this version can be reproduced by building from source code at commit d04984a associated with the tag v_1.5.38. Release built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

2026-06-26 Release of logback version 1.5.37

1. • Given the numerous vulnerabilities related to conditional configuration processing based on the evaluation of Java expressions using the Janino library, support for such expressions has been removed. Users are offered the an online migration service or the <condition> element introduced in version 1.5.20. See the relevant documentation for more details.

• A bitwise identical binary of this version can be reproduced by building from source code at commit c1df7f5 associated with the tag v_1.5.37. Release built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.

2026-06-25 Release of logback version 1.5.36

• The 'condition' attribute in <if> elements now reject certain references that are associated with ACE attacks. This issue was reported by "yulate" (yulate531@gmail.com.com) and registered as CVE-2026-13006. Please note that version 1.5.37 provides the full fix to this vulnerability.

• A bitwise identical binary of this version can be reproduced by building from source code at commit 9b94c37 associated with the tag v_1.5.36. Release built using Java "21" 2023-10-17 LTS build 21.0.1.+12-LTS-29 under Linux Debian 11.6.