[dependabot]

Bumps ch.qos.logback:logback-classic from 1.2.3 to 1.6.6.

Release notes

Sourced from ch.qos.logback:logback-classic's releases.

Logback 1.6.6

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](qos-ch/logback#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](qos-ch/logback#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](qos-ch/logback#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](qos-ch/logback#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 a9ee8019ee183e076ff5477957dbf90c4b04dd92 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.

Logback 1.6.5

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 d1b829dcdb9fd98511c64401beb1419a9c9384aa 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.

Logback 1.6.4

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.

... (truncated)

Commits

• a9ee801 prepare release 1.6.6
• 7fa8e8e throw ScanException on unmatched '}' during variable substitution, fixes #836
• 355b931 Test round trip of circular exceptions through LoggingEventVO
• c7b8e2f reject cyclic throwable proxies in LoggingEventVO.readObject
• 6217f11 fix loging of ThrowableProxy constructor taking isCyclic boolean
• 0b95858 LOGBACK-1337 LogbackMDCAdapter should store mdc in LinkedHashMap to predict o...
• 5c1f577 add LinkedHashMap to HardenedObjectInputStream whitelist
• 7c36c71 Escape regex metacharacters in date patterns, harden rolling tests
• d268774 Align date pattern to regex conversion with DateTimeFormatter
• b4b4828 Escape regex metacharacters of literal text in FileNamePattern regexes
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot show <dependency name> ignore conditions will show all of the ignore conditions of the specified dependency
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Apart from the inline findings, I checked whether this bump affects consumers' Java 8 floor. It doesn't: logback-classic is declared only as testImplementation (build.gradle:44), so the published artifact and the sourceCompatibility/targetCompatibility 1.8 pins are unchanged.

Extended reasoning...

The change bumps one version string in build.gradle: the test-only logback-classic goes from 1.2.3 to 1.6.6. It touches no security-sensitive code. Because logback 1.6.x needs a newer JDK than Java 8, I checked the dependency's scope and found it is test-only, so the newer JDK requirement affects only the JDK 17 test build and not consumers.

[claude]

🟡 nit (optional): After this bump, build.gradle declares two different logback versions: logback-classic at 1.6.6 and logback-core at 1.6.3. The two are released together as a matched pair. Gradle quietly resolves logback-core to 1.6.6 through logback-classic's own dependency, so slf4j_core_version = "1.6.3" no longer says what the tests actually run with. Fix: bump slf4j_core_version to "1.6.6" as well. Better still, drive both artifacts from a single logback_version variable so later Dependabot bumps cannot split them.

Why this was flagged

build.gradle:43 uses slf4j_core_version (still "1.6.3") for ch.qos.logback:logback-core. build.gradle:44 now uses slf4j_classic_version ("1.6.6") for ch.qos.logback:logback-classic. On the base branch both declarations were older but separate as well. This PR makes the two halves of one library disagree on patch level. With a plain version string, Gradle's conflict resolution upgrades logback-core to the 1.6.6 that logback-classic requires transitively, so test runs still work. The declared 1.6.3 is therefore stale and misleading. A later edit that pins it strictly, or a separate Dependabot PR for logback-core, could leave mismatched logback-core/logback-classic jars on the test classpath. Only test scope is affected, and published consumers are not.

Verification: In build.gradle, line 29 still has slf4j_core_version = "1.6.3", which line 43 uses for logback-core. Line 30 now has slf4j_classic_version = "1.6.6", which line 44 uses for logback-classic. Gradle's default conflict resolution picks the highest version, so the test classpath gets logback-core 1.6.6. This PR is what makes line 43 a dead declaration.

_{Finding ID: f-687bddef}

[claude]

🟡 nit (optional): This bump adds no CHANGELOG.md entry, so the next release note will not mention it. AGENTS.md and CONTRIBUTING.md:52 ask every change to add a line under ## [Unreleased], because release automation only renames that heading. Fix: add a line under ## [Unreleased] in CHANGELOG.md, e.g. "Bump test dependency ch.qos.logback:logback-classic from 1.2.3 to 1.6.6". Put it under a section such as ### Fixed, which earlier releases used for non-API changes like "Pin conventional commits (#21)".

Why this was flagged

The diff changes only build.gradle:30 (slf4j_classic_version "1.2.3" -> "1.6.6"). CHANGELOG.md is untouched, and its ## [Unreleased] heading at CHANGELOG.md:8 is still empty. AGENTS.md:81-84 and CONTRIBUTING.md:52 say release automation only renames ## [Unreleased] and never writes entries, so a change with no entry ships with an empty release note. Once this merges, the next release's notes leave out this dependency change. The base branch has no such gap because the change does not exist there. No CI check enforces changelog entries, and Dependabot PRs are exempt from the title and branch checks (AGENTS.md Gotchas 3), so nothing catches the omission.

Verification: Severity: nit. The trigger is merging this PR as it stands, which changes only slf4j_classic_version = "1.2.3" to "1.6.6" at build.gradle line 30. CHANGELOG.md is untouched, and its ## [Unreleased] heading at CHANGELOG.md:8 has no entries. AGENTS.md:81-83 and CONTRIBUTING.md:52 require a hand-written entry. The next release note leaves out this bump.

_{Finding ID: f-f1f2d09d}