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NVD / CVE Program· CNA mozilla

CVE-2023-6857: When resolving a symlink, a race may occur where the buffer passed to `readlink` may actually be smaller than necessary.

Noroxi assessment

Priority: Monitor (action score 21/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.66% (FIRST EPSS); higher than 51.7% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. Special conditions such as timing or configuration are required.
  • Fixed version: firefox (AlmaLinux:8) 115.6.0-1.el8_9.alma; thunderbird (AlmaLinux:8) 115.6.0-1.el8_9.alma; firefox (AlmaLinux:9) 115.6.0-1.el9_3.alma.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to firefox (AlmaLinux:8) 115.6.0-1.el8_9.alma; thunderbird (AlmaLinux:8) 115.6.0-1.el8_9.alma; firefox (AlmaLinux:9) 115.6.0-1.el9_3.alma or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

When resolving a symlink, a race may occur where the buffer passed to `readlink` may actually be smaller than necessary. *This bug only affects Firefox on Unix-based operating systems (Android, Linux, MacOS). Windows is unaffected.* This vulnerability affects Firefox ESR < 115.6, Thunderbird < 115.6, and Firefox < 121.

MediumCVSS 5.3 · v3.1—No exploit Fix available
Published
Dec 19, 2023
Updated
Jun 17, 2026
EPSS
0.6% · 51th percentile

Report tools

JSON

Action score

21

Monitor

Low priority for now.

CVSS
21 / 40 · 5.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.6%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2023-6857

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
mozillafirefox
mozillafirefox esr
mozillathunderbird
applemacos
googleandroid
linuxlinux kernel
debiandebian linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • debian debian linux10.0
  • debian debian linux11.0
  • debian debian linux12.0
  • mozilla firefoxbefore 121.0
  • mozilla firefox esrbefore 115.6
  • mozilla thunderbirdbefore 115.6

Versions reported by the vendor

Affected version ranges reported by the assigning authority (mozilla). Independent of NVD's CPE analysis and usually ahead of it.

  • Mozilla Firefox

    • unspecified and later · before 121affected

  • Mozilla Firefox ESR

    • unspecified and later · before 115.6affected

  • Mozilla Thunderbird

    • unspecified and later · before 115.6affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:8firefoxbefore 115.6.0-1.el8_9.alma115.6.0-1.el8_9.alma
AlmaLinux:8thunderbirdbefore 115.6.0-1.el8_9.alma115.6.0-1.el8_9.alma
AlmaLinux:9firefoxbefore 115.6.0-1.el9_3.alma115.6.0-1.el9_3.alma
AlmaLinux:9firefox-x11before 115.6.0-1.el9_3.alma115.6.0-1.el9_3.alma
AlmaLinux:9thunderbirdbefore 115.6.0-1.el9_3.alma115.6.0-1.el9_3.alma
Debian:10firefox-esrbefore 115.6.0esr-1~deb10u1115.6.0esr-1~deb10u1
Debian:10thunderbirdbefore 1:115.6.0-1~deb10u11:115.6.0-1~deb10u1
Debian:11firefox-esrbefore 115.6.0esr-1~deb11u1115.6.0esr-1~deb11u1
Debian:11thunderbirdbefore 1:115.6.0-1~deb11u11:115.6.0-1~deb11u1
Debian:12firefox-esrbefore 115.6.0esr-1~deb12u1115.6.0esr-1~deb12u1
Debian:12thunderbirdbefore 1:115.6.0-1~deb12u11:115.6.0-1~deb12u1
Debian:13firefox-esrbefore 115.6.0esr-1115.6.0esr-1
Debian:13thunderbirdbefore 1:115.6.0-11:115.6.0-1
openSUSE:Leap 15.4MozillaFirefoxbefore 115.6.0-150200.152.120.1115.6.0-150200.152.120.1
openSUSE:Leap 15.5MozillaThunderbirdbefore 115.6.0-150200.8.142.2115.6.0-150200.8.142.2
openSUSE:TumbleweedMozillaFirefoxbefore 121.0-1.1121.0-1.1
openSUSE:TumbleweedMozillaThunderbirdbefore 115.6.0-1.1115.6.0-1.1
Red Hat:enterprise_linux:7::clientfirefoxbefore 0:115.6.0-1.el7_90:115.6.0-1.el7_9
Red Hat:enterprise_linux:7::clientfirefox-debuginfobefore 0:115.6.0-1.el7_90:115.6.0-1.el7_9
Red Hat:enterprise_linux:7::clientthunderbirdbefore 0:115.6.0-1.el7_90:115.6.0-1.el7_9
Red Hat:enterprise_linux:7::clientthunderbird-debuginfobefore 0:115.6.0-1.el7_90:115.6.0-1.el7_9
Red Hat:enterprise_linux:8::appstreamfirefoxbefore 0:115.6.0-1.el8_90:115.6.0-1.el8_9
Red Hat:enterprise_linux:8::appstreamfirefox-debuginfobefore 0:115.6.0-1.el8_90:115.6.0-1.el8_9
Red Hat:enterprise_linux:8::appstreamfirefox-debugsourcebefore 0:115.6.0-1.el8_90:115.6.0-1.el8_9

+53

Same product

mozilla: all records

Other highest-scoring records for the same primary product.

  • CVE-2010-3765Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x befKEV
    94Now
  • CVE-2019-11708Insufficient vetting of parameters passed with the Prompt:Open IPC message between child and parent processes can result in the non-sandboxeKEV
    87Now
  • CVE-2015-4495The PDF reader in Mozilla Firefox before 39.0.3, Firefox ESR 38.x before 38.1.1, and Firefox OS before 2.2 allows remote attackers to bypassKEV
    86Now

Published before and after this one in the same product

  • ← EarlierCVE-2023-6135Dec 19, 2023 · Multiple NSS NIST curves were susceptible to a side-channel attack known as "Minerva".
    17Monitor
  • ← EarlierCVE-2023-6856Dec 19, 2023 · The WebGL `DrawElementsInstanced` method was susceptible to a heap buffer overflow when used on systems with the Mesa VM driver.
    41Plan
  • Later →CVE-2023-6858Dec 19, 2023 · Firefox was susceptible to a heap buffer overflow in `nsTextFragment` due to insufficient OOM handling.
    35Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:firefox115.6.0-1.el8_9.alma · AlmaLinux:8Package registry (OSV)
almalinux:firefox-x11115.6.0-1.el9_3.alma · AlmaLinux:9Package registry (OSV)
almalinux:thunderbird115.6.0-1.el9_3.alma · AlmaLinux:9Package registry (OSV)
debian:firefox-esr115.6.0esr-1~deb12u1 · Debian:12Package registry (OSV)
debian:thunderbird1:115.6.0-1~deb12u1 · Debian:12Package registry (OSV)
opensuse:MozillaFirefox115.6.0-150200.152.120.1 · openSUSE:Leap 15.4Package registry (OSV)
opensuse:MozillaThunderbird115.6.0-150200.8.142.2 · openSUSE:Leap 15.5Package registry (OSV)
red hat:firefox0:115.6.0-1.el8_8 · Red Hat:rhel_eus:8.8::appstreamPackage registry (OSV)
red hat:firefox-debuginfo0:115.6.0-1.el8_8 · Red Hat:rhel_eus:8.8::appstreamPackage registry (OSV)
red hat:firefox-debugsource0:115.6.0-1.el8_8 · Red Hat:rhel_eus:8.8::appstreamPackage registry (OSV)
red hat:firefox-x110:115.6.0-1.el9_2 · Red Hat:rhel_eus:9.2::appstreamPackage registry (OSV)
red hat:thunderbird0:115.6.0-1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:thunderbird-debuginfo0:115.6.0-1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:thunderbird-debugsource0:115.6.0-1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
rocky linux:firefox0:115.6.0-1.el8_9 · Rocky Linux:8Package registry (OSV)
rocky linux:thunderbird0:115.6.0-1.el8_9 · Rocky Linux:8Package registry (OSV)
suse:MozillaFirefox115.6.0-112.194.1 · SUSE:Linux Enterprise Software Development Kit 12 SP5Package registry (OSV)
suse:MozillaFirefox115.6.0-150200.152.120.1 · SUSE:Linux Enterprise Module for Desktop Applications 15 SP4Package registry (OSV)
suse:MozillaThunderbird115.6.0-150200.8.142.2 · SUSE:Linux Enterprise Module for Package Hub 15 SP5Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2022-22763362 days apartWhen a worker is shutdown, it was possible to cause script to run late in the lifecycle, at a point after where it should not be possible.
    35Monitor
  • CVE-2023-29537200 days apartMultiple race conditions in the font initialization could have led to memory corruption and execution of attacker-controlled code.
    30Monitor
  • CVE-2022-22737362 days apartConstructing audio sinks could have lead to a race condition when playing audio files and closing windows.
    30Monitor
  • CVE-2022-42930362 days apartIf two Workers were simultaneously initializing their CacheStorage, a data race could have occurred in the `ThirdPartyUtil` component.
    28Monitor
  • CVE-2024-9936300 days apartWhen manipulating the selection node cache, an attacker may have been able to cause unexpected behavior, potentially leading to an exploitab
    26Monitor
  • CVE-2024-11708343 days apartMissing thread synchronization primitives could have led to a data race on members of the PlaybackParams structure.
    26Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • A user must open a link or visit a page.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
none
Integrity
high · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality impact
None
Integrity impact
High
Availability impact
None

Weakness class (CWE)

CWE-362 · Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (8 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records