# What is CVE-2021-33037?

> CVE-2021-33037 is a medium-severity flaw (CVSS 5.3) in Tomcat from Apache, published on 12 July 2021. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 75%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-33037

## At a glance

- **Verdict:** Fix this soon. Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month.
- **Precursor Intelligence risk score:** 53 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** Medium (CVSS 5.3 out of 10)
- **Known to be exploited:** No, not on the list of flaws known to be exploited today
- **Chance of use in the next 30 days:** 75% (latest exploit-likelihood forecast)
- **Published:** 12 July 2021
- **Record last updated:** 7 November 2023
- **Main product:** Tomcat from Apache
- **Affected products:** 22

## What is CVE-2021-33037? In plain terms

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can change some data.

### The official description

Apache Tomcat 10.0.0-M1 to 10.0.6, 9.0.0.M1 to 9.0.46 and 8.5.0 to 8.5.66 did not correctly parse the HTTP transfer-encoding request header in some circumstances leading to the possibility to request smuggling when used with a reverse proxy. Specifically: - Tomcat incorrectly ignored the transfer encoding header if the client declared it would only accept an HTTP/1.0 response; - Tomcat honoured the identify encoding; and - Tomcat did not ensure that, if present, the chunked encoding was the final encoding.

### What kind of flaw is it?

- CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Easy: no special conditions
- Login needed first: No login needed
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can change some data

Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`

## Is CVE-2021-33037 being exploited? Not that we know of

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 75%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 75%, 75%, 75%, 75%, 75%, 75%, 75%.

### Timeline

- 12 July 2021: Published
- 7 November 2023: Record last updated
- 19 November 2025: Exploit likelihood jumped
- 22 November 2025: Exploit likelihood fell

### How Precursor Intelligence ranks it

CVE-2021-33037 scores **53 out of 100 (Medium)**, with the action "Plan remediation".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: smaller factor
- Threat activity around it: smaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2021-33037?

The published record lists 22 products. Versions are as published: "before 5.10.0" means every version up to, but not including, 5.10.0.

- [Tomcat](https://www.precursorintelligence.com/product/apache/tomcat) by [Apache](https://www.precursorintelligence.com/vendors/apache) (Application): 8.5.0 to 8.5.66, after 9.0.0 to 9.0.46, after 10.0.0 to 10.0.6
- [Epolicy Orchestrator](https://www.precursorintelligence.com/product/mcafee/epolicy_orchestrator) by [Mcafee](https://www.precursorintelligence.com/vendors/mcafee) (Application): before 5.10.0, 5.10.0, 5.10.0-update_1, 5.10.0-update_2, 5.10.0-update_3, 5.10.0-update_4, 5.10.0-update_5, 5.10.0-update_6, 5.10.0-update_7, 5.10.0-update_8, 5.10.0-update_9, 5.10.0-update_10
- [Instantis Enterprisetrack](https://www.precursorintelligence.com/product/oracle/instantis_enterprisetrack) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 17.1, 17.2, 17.3
- [Utilities Testing Accelerator](https://www.precursorintelligence.com/product/oracle/utilities_testing_accelerator) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 6.0.0.1.1, 6.0.0.2.2, 6.0.0.3.1
- [Debian Linux](https://www.precursorintelligence.com/product/debian/debian_linux) by [Debian](https://www.precursorintelligence.com/vendors/debian) (Operating system): 9.0, 10.0
- [Managed File Transfer](https://www.precursorintelligence.com/product/oracle/managed_file_transfer) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 12.2.1.3.0, 12.2.1.4.0
- [SD-WAN Edge](https://www.precursorintelligence.com/product/oracle/sd-wan_edge) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 9.0, 9.1
- [Agile Plm](https://www.precursorintelligence.com/product/oracle/agile_plm) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 9.3.6
- [Communications Cloud Native Core Policy](https://www.precursorintelligence.com/product/oracle/communications_cloud_native_core_policy) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 1.14.0
- [Communications Cloud Native Core Service Communication Proxy](https://www.precursorintelligence.com/product/oracle/communications_cloud_native_core_service_communication_proxy) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 1.14.0
- [Communications Diameter Signaling Router](https://www.precursorintelligence.com/product/oracle/communications_diameter_signaling_router) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 8.0.0.0 to 8.5.0.2
- [Communications Instant Messaging Server](https://www.precursorintelligence.com/product/oracle/communications_instant_messaging_server) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 10.0.1.5.0
- [Communications Policy Management](https://www.precursorintelligence.com/product/oracle/communications_policy_management) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 12.5.0
- [Communications Pricing Design Center](https://www.precursorintelligence.com/product/oracle/communications_pricing_design_center) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 12.0.0.3.0
- [Communications Session Report Manager](https://www.precursorintelligence.com/product/oracle/communications_session_report_manager) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 8.0.0 to 8.2.4.0
- [Communications Session Route Manager](https://www.precursorintelligence.com/product/oracle/communications_session_route_manager) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 8.0.0 to 8.2.4
- [Graph Server and Client](https://www.precursorintelligence.com/product/oracle/graph_server_and_client) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): before 21.4
- [Healthcare Translational Research](https://www.precursorintelligence.com/product/oracle/healthcare_translational_research) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 4.1.0
- [Hospitality Cruise Shipboard Property Management System](https://www.precursorintelligence.com/product/oracle/hospitality_cruise_shipboard_property_management_system) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 20.1.0
- [Mysql Enterprise Monitor](https://www.precursorintelligence.com/product/oracle/mysql_enterprise_monitor) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): up to 8.0.25
- [Secure Global Desktop](https://www.precursorintelligence.com/product/oracle/secure_global_desktop) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 5.6
- [Tomee](https://www.precursorintelligence.com/product/apache/tomee) by [Apache](https://www.precursorintelligence.com/vendors/apache) (Application): 8.0.6

## How do I fix CVE-2021-33037?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

### References

- [oracle.com](https://www.oracle.com//security-alerts/cpujul2021.html) (Patch, Third-party advisory)
- [oracle.com](https://www.oracle.com/security-alerts/cpuapr2022.html) (Patch, Third-party advisory)
- [oracle.com](https://www.oracle.com/security-alerts/cpujan2022.html) (Patch, Third-party advisory)
- [oracle.com](https://www.oracle.com/security-alerts/cpuoct2021.html) (Patch, Third-party advisory)
- [lists.apache.org](https://lists.apache.org/thread.html/r612a79269b0d5e5780c62dfd34286a8037232fec0bc6f1a7e60c9381%40%3Cannounce.tomcat.apache.org%3E) (Mailing list, Vendor advisory)
- [kc.mcafee.com](https://kc.mcafee.com/corporate/index?page=content&id=SB10366) (Third-party advisory)
- [lists.apache.org](https://lists.apache.org/thread.html/r290aee55b72811fd19e75ac80f6143716c079170c5671b96932ed44b%40%3Ccommits.tomee.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r40f921575aee8d7d34e53182f862c45cbb8f3d898c9d4e865c2ec262%40%3Ccommits.tomee.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/rc6ef52453bb996a98cb45442871a1db56b7c349939e45d829bf9ae37%40%3Ccommits.tomee.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/rd0dfea39829bc0606c936a16f6fca338127c86c0a1083970b45ac8d2%40%3Ccommits.tomee.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/re01e7e93154e8bdf78a11a23f9686427bd3d51fc6e12c508645567b7%40%3Ccommits.tomee.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/rf1b54fd3f52f998ca4829159a88cc4c23d6cef5c6447d00948e75c97%40%3Ccommits.tomee.apache.org%3E)
- [lists.debian.org](https://lists.debian.org/debian-lts-announce/2021/08/msg00009.html) (Mailing list, Third-party advisory)
- [security.gentoo.org](https://security.gentoo.org/glsa/202208-34) (Third-party advisory)
- [security.netapp.com](https://security.netapp.com/advisory/ntap-20210827-0007/) (Third-party advisory)
- [debian.org](https://www.debian.org/security/2021/dsa-4952) (Third-party advisory)

## Questions

### What is CVE-2021-33037?

CVE-2021-33037 is a medium-severity flaw in Tomcat from Apache, published on 12 July 2021. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can change some data.

### How serious is CVE-2021-33037?

It scores 5.3 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2021-33037 is 53 out of 100, which is Medium. Its action is "Plan remediation". Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month.

### Is CVE-2021-33037 being exploited?

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 75%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2021-33037 affect?

For Tomcat from Apache: 8.5.0 to 8.5.66, after 9.0.0 to 9.0.46, after 10.0.0 to 10.0.6. The record lists 22 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2021-33037?

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2021-33037 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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