8.1

CVE-2021-29991: mozilla firefox HTTP Request/Response Smuggling

CVSS: 8.1v3.1HighModified
AliasesUBUNTU-CVE-2021-29991USN-5047-1
Published 03-11-2021Last modified 03-08-2024
Open JSON

Vulnerability summary

CVE-2021-29991 is a high (CVSS 8.1) HTTP Request/Response Smuggling vulnerability in mozilla firefox. EPSS estimates a 0.91% chance of exploitation in the next 30 days, higher than 59.3% of scored vulnerabilities.

Overall risk
33/100
0100
Medium · default modelHow is this calculated?
CVSS score
8.1/10
010
High · v3.1 (NVD)
EPSS score
0.91%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 17 · Related 17
OPENSUSE-SU-2021:1367-1OPENSUSE-SU-2021:1635-1OPENSUSE-SU-2021:3331-1OPENSUSE-SU-2021:3451-1OPENSUSE-SU-2021:4150-1OPENSUSE-SU-2024:10600-1

Timeline

  1. 03-11-2021
    PublishedVulnerability first disclosed.
  2. 03-08-2024
    Last modifiedVulnerability information updated.

Description

Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers. This allowed for a header splitting attack against servers using HTTP/3. This vulnerability affects Firefox < 91.0.1 and Thunderbird < 91.0.1.

CVSS metrics

3 scores · 2 sources · 2 versions

EPSS trend

Probability

0.91%

Chance of exploitation in the next 30 days

Percentile

59%

Versus all other CVEs

30-day change

0.00 pp

From 0.91% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.91%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Ubuntu6 products
  • firefox< 91.0.1+build1-0ubuntu0.18.04.1 | < 91.0.1+build1-0ubuntu0.20.04.1
  • mozjs38All versions (No fix recorded)
  • mozjs52All versions (No fix recorded)
  • mozjs68All versions (No fix recorded)
  • mozjs78All versions (No fix recorded)
Mozilla2 products
  • firefox≥ unspecified, < 91.0.1 | < 91.0.1
  • thunderbird≥ unspecified, < 91.0.1 | < 91.0.1

2 vendors · 8 products

References

7 links