Patch Tuesday (also known as Update Tuesday) is an unofficial term used to refer to when Microsoft, Adobe, Oracle and others regularly releases software patches for their software products. It is widely referred to in this way by the industry. Microsoft formalized Patch Tuesday in October 2003. Patch Tuesday is known within Microsoft also as the "B" release, to distinguish it from the "C" and "D" releases that occur in the third and fourth weeks of the month, respectively.
Patch Tuesday occurs on the second, and sometimes fourth, Tuesday of each month in North America. As far as the integrated Windows Update (WU) function is concerned, Patch Tuesday begins at 18:00 or 17:00 UTC (10:00 PST (UTC-8) or 10:00 PDT (UTC-7)). The updates show up in Download Center before they are added to WU, and the KB articles and the Technet bulletin are unlocked later.
Microsoft has a pattern of releasing a larger number of updates in even-numbered months, and fewer in odd-numbered months. Minor updates are also released outside Patch Tuesday. Daily updates consist of malware database refreshes for Windows Defender and Microsoft Security Essentials. Sometimes there is an extraordinary Patch Tuesday, two weeks after the regular Patch Tuesday. Some updates could be released at any time.
Starting with Windows 98, Microsoft included Windows Update that once installed and executed, would check for patches to Windows and its components, which Microsoft would release intermittently. With the release of Microsoft Update, this system also checks for updates for other Microsoft products, such as Microsoft Office, Visual Studio and SQL Server.
Earlier versions of Windows Update suffered from two problems:
Microsoft introduced "Patch Tuesday" in October 2003 to reduce the cost of distributing patches. This system accumulates security patches over a month, and dispatches them all on the second Tuesday of each month, an event for which system administrators may prepare. The following day, informally known as "Exploit Wednesday", marks the time when exploits may appear in the wild which take advantage on unpatched machines of the newly announced vulnerabilities.
Tuesday was chosen as the optimal day of the week to distribute software patches. This is done to maximize the amount of time available before the upcoming weekend to correct any issues that might arise with those patches, while leaving Monday free to address other unexpected issues that might have arisen over the preceding weekend.
An obvious security implication is that security problems that have a solution are withheld from the public for up to a month. This policy is adequate when the vulnerability is not widely known or is extremely obscure, but that is not always the case.
There have been cases where vulnerability information became public or actual worms were circulating prior to the next scheduled Patch Tuesday. In critical cases Microsoft issues corresponding patches as they become ready, alleviating the risk if updates are checked for and installed frequently.
At the Ignite 2015 event, Microsoft revealed a change in distributing security patches. They release security updates to home PCs, tablets and phones as soon as they are ready, while enterprise customers will stay on the monthly update cycle, which was reworked as Windows Update for Business.
Many exploitation events are seen shortly after the release of a patch; analysis of the patch helps exploit developers to immediately take advantage of the previously undisclosed vulnerability, which will remain in unpatched systems. Therefore, the term "Exploit Wednesday" was coined.
Microsoft warned users that it discontinued support for Windows XP starting on April 8, 2014 – users running Windows XP afterwards would be at the risk of attacks. As security patches of newer Windows versions can reveal similar (or same) vulnerabilities present in both newer and older Windows versions, this can allow attacks on devices with unsupported Windows versions (cf. "zero-day attacks"). However Microsoft stopped fixing such (and other) vulnerabilities in unsupported Windows versions, regardless how widely known such vulnerabilities became, leaving these vulnerabilities unfixed and devices running these Windows versions vulnerable to attacks. Microsoft made a singular exception during the rapid spread of the WannaCry ransomware and released patches in May 2017 for the by then-unsupported Windows XP, Windows 8, and Windows Server 2003 (in addition to then supported Windows versions).
For Windows 7 (including Service Pack 1), support ended January 14, 2020, and on January 10, 2023 for Windows 8.1; this will cause the same "unfixed vulnerabilities" issue for users of these operating systems. Support for Windows 8 already ended January 12, 2016 (with users having to install Windows 8.1 or Windows 10 to continue to get support), and support for Windows 7 without SP1 was ended April 9, 2013 (with the ability to install SP1 to continue to get support until 2020, or having to install Windows 8.1 or Windows 10 to receive support after 2020).
One major change with the introduction of Windows 10 was that Microsoft started to release a new version of Windows 10 twice per year, and with Microsoft's "modern lifecycle policy" a newly released Windows 10 version starts a "grace period" for the previous version with regard to support – unlike previous Windows products which received only infrequent updates via service packs, and support was governed by the "fixed lifecycle policy". With this new policy Home and Pro versions of Windows 10 will be provided with security and feature updates (so called "mainstream support") for up to 18 months after release, "enterprise" and education versions for 24 months. To give an example: support for Windows 10 Home/Pro version 1703 (which was released in April 2017) was stopped by Microsoft in October 2018, and support for versions 1507 and 1511 (released in 2015) officially ended in 2017. Microsoft announced that it would give "extended support" (security but not feature updates) for at least one "semi-annual channel" (SAC) Windows 10 version until October 14, 2025.
According to Microsoft a "device needs to install the latest version (feature update) before [the] current version reaches end of service to help keep your device secure and have it remain supported by Microsoft". As with previous Windows operating systems, any device running such an unsupported version of Windows (which no longer receives security patches) is potentially affected by the "unfixed vulnerabilities" issue beginning with the "end of support" date. To counter this Microsoft has designed the update system for the Home and Pro editions of Windows 10 so that in most cases if technically possible the latest Windows version is downloaded and installed automatically – this has however drawn criticism due to other problems such forced upgrades can introduce.
|Version||Codename||Marketing name||Build||Release date||Support until (and support status by color)|
|1507||Threshold 1||N/A||10240||July 29, 2015||May 9, 2017||October 14, 2025||N/A|
|1511||Threshold 2||November Update||10586||November 10, 2015||October 10, 2017||April 10, 2018||N/A||January 9, 2018|
|1607||Redstone 1||Anniversary Update||14393||August 2, 2016||April 10, 2018[b]||April 9, 2019[b]||October 13, 2026||October 9, 2018|
|1703||Redstone 2||Creators Update||15063||April 5, 2017[c]||October 9, 2018[d]||October 8, 2019[d]||N/A||June 11, 2019|
|1709||Redstone 3||Fall Creators Update||16299[e]||October 17, 2017||April 9, 2019||October 13, 2020[f]||January 14, 2020|
|1803||Redstone 4||April 2018 Update||17134||April 30, 2018||November 12, 2019||May 11, 2021[g]||N/A|
|1809||Redstone 5||October 2018 Update||17763||November 13, 2018[h]||November 10, 2020[i]||January 9, 2029|
|1903||19H1||May 2019 Update||18362||May 21, 2019||December 8, 2020||N/A|
|1909||19H2||November 2019 Update||18363||November 12, 2019||May 11, 2021||May 10, 2022|
|2004||20H1||May 2020 Update||19041||May 27, 2020||December 14, 2021|
|20H2||20H2||October 2020 Update||19042||October 20, 2020||May 10, 2022||May 9, 2023|
|21H1||21H1||May 2021 Update||19043||May 18, 2021||December 13, 2022|
In addition to the commonly used editions like Home and Pro, Microsoft offers specialized "Long-Term Servicing Branch" (LTSB) or "Long-Term Servicing Channel" (LTSC) versions of Windows 10 with longer support timelines, governed by Microsoft's "fixed lifecycle policy", e.g. "Windows 10 Enterprise 2016 LTSB" will receive extended support until October 13, 2026, and "Windows 10 2019 LTSC" will receive extended support until January 9, 2029.
SAP's "Security Patch Day", when the company advises users to install security updates, was chosen to coincide with Patch Tuesdays. Adobe Systems' update schedule for Flash Player since November 2012 also coincides with Patch Tuesday. One of the reasons for this is that Flash Player comes as part of Windows starting with Windows 8 and Flash Player updates for the built-in and the plugin based version both need to be published at the same time in order to prevent reverse-engineering threats. Oracle's quarterly updates coincide with Patch Tuesday.
Windows Update uses the Background Intelligent Transfer Service (BITS) to download the updates, using idle network bandwidth. However BITS will use the speed as reported by the network interface (NIC) to calculate bandwidth. This can lead to bandwidth calculation errors, for example when a fast network adapter (e.g. 10 Mbit/s) is connected to the network via a slow link (e.g. 56 kbit/s) – according to Microsoft "BITS will compete for the full bandwidth [of the NIC] ... BITS has no visibility of the network traffic beyond the client."
Furthermore, the Windows Update servers of Microsoft do not honor the TCP's slow-start congestion control strategy. As a result, other users on the same network may experience significantly slower connections from machines actively retrieving updates. This can be particularly noticeable in environments where many machines individually retrieve updates over a shared, bandwidth-constrained link such as those found in many multi-PC homes and small to medium-sized businesses. Bandwidth demands of patching large numbers of computers can be reduced significantly by deploying Windows Server Update Services (WSUS) to distribute the updates locally.
In addition to updates being downloaded from Microsoft servers, Windows 10 devices can "share" updates in a peer-to-peer fashion with other Windows 10 devices on the local network, or even with Windows 10 devices on the internet. This can potentially distribute updates faster while reducing usage for networks with a metered connection.