# What is CVE-2019-17638?

> CVE-2019-17638 is a critical-severity flaw (CVSS 9.4) in Jetty from Eclipse, published on 9 July 2020. 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 11%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2019-17638

## 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:** 54 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** Critical (CVSS 9.4 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:** 11% (latest exploit-likelihood forecast)
- **Published:** 9 July 2020
- **Record last updated:** 7 November 2023
- **Main product:** Jetty from Eclipse
- **Affected products:** 1

## What is CVE-2019-17638? 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 read data and change data.

### The official description

In Eclipse Jetty, versions 9.4.27.v20200227 to 9.4.29.v20200521, in case of too large response headers, Jetty throws an exception to produce an HTTP 431 error. When this happens, the ByteBuffer containing the HTTP response headers is released back to the ByteBufferPool twice. Because of this double release, two threads can acquire the same ByteBuffer from the pool and while thread1 is about to use the ByteBuffer to write response1 data, thread2 fills the ByteBuffer with other data. Thread1 then proceeds to write the buffer that now contains different data. This results in client1, which issued request1 seeing data from another request or response which could contain sensitive data belonging to client2 (HTTP session ids, authentication credentials, etc.). If the Jetty version cannot be upgraded, the vulnerability can be significantly reduced by configuring a responseHeaderSize significantly larger than the requestHeaderSize (12KB responseHeaderSize and 8KB requestHeaderSize).

### What kind of flaw is it?

- CWE-672: Operation on a Resource after Expiration or Release
- CWE-675: Multiple Operations on Resource in Single-Operation Context

### 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 read data and change data

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

## Is CVE-2019-17638 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 11%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 11%, 11%, 11%, 11%, 11%, 11%, 11%.

### Timeline

- 9 July 2020: Published
- 7 November 2023: Record last updated
- 16 June 2026: Exploit likelihood fell

### How Precursor Intelligence ranks it

CVE-2019-17638 scores **54 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-2019-17638?

The published record lists 1 product.

- [Jetty](https://www.precursorintelligence.com/product/eclipse/jetty) by [Eclipse](https://www.precursorintelligence.com/vendors/eclipse) (Application): 9.4.27-20200227, 9.4.28-20200408, 9.4.29-20200521

## How do I fix CVE-2019-17638?

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 advisory 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

- [bugs.eclipse.org](https://bugs.eclipse.org/bugs/show_bug.cgi?id=564984) (Vendor advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2020/08/17/1)
- [lists.apache.org](https://lists.apache.org/thread.html/r29073905dc9139d0d7a146595694bf57bb9e35e5ec6aa73eb9c8443a%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r378e4cdec15e132575aa1dcb6296ffeff2a896745a8991522e266ad4%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r4bdd3f7bb6820a79f9416b6667d718a06d269018619a75ce4b759318%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r521168299e023fb075b57afe33d17ff1d09e8a10e0fd8c775ea0e028%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r7fc5f2ed49641ea91c433e3cd0fc3d31c0278c87b82b15c33b881415%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r81f58591fb4716fb867b36956f30c7c8ad4ab3f23abc952d9d86a2a0%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r9584c4304c888f651d214341a939bd264ed30c9e3d0d30fe85097ecf%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/r9a2cfa56d30782a0c17a5deb951a622d1f5c8de48e1c3b578ffc2a84%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/ra8661fc8c69c647cb06153c1485d48484a833d873f75dfe45937e9de%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/rbe1f230e87ea947593145d0072d0097ddb0af10fee1161db8ca1546c%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/rd0e44e8ef71eeaaa3cf3d1b8b41eb25894372e2995ec908ce7624d26%40%3Ccommits.pulsar.apache.org%3E)
- [lists.apache.org](https://lists.apache.org/thread.html/rd98cfd012490cb02caa1a11aaa0cc38bff2d43bcce9b20c2f01063dd%40%3Ccommits.pulsar.apache.org%3E)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XE6US6VPZHOWFMUSFGDS5V2DNQPY5MKB/)
- [oracle.com](https://www.oracle.com/security-alerts/cpuApr2021.html)
- [oracle.com](https://www.oracle.com/security-alerts/cpuoct2020.html)

## Questions

### What is CVE-2019-17638?

CVE-2019-17638 is a critical-severity flaw in Jetty from Eclipse, published on 9 July 2020. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data and change data.

### How serious is CVE-2019-17638?

It scores 9.4 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2019-17638 is 54 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-2019-17638 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 11%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2019-17638 affect?

For Jetty from Eclipse: 9.4.27-20200227, 9.4.28-20200408, 9.4.29-20200521.

### How do I fix CVE-2019-17638?

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-2019-17638 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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